Greenhouse Tips and General Information

Do you love plants and gardening?  Then you may want to consider a personal-sized greenhouse to extend your green thumb endeavors.

Greenhouses come in many sizes - the greenhouse you consider might be an 18 by 24 foot (five by seven meter) unit in your backyard. A greenhouse this size will hold many plants, which can require a good bit of time on a fairly regular basis. The size of the greenhouse is a factor in how much of a time investment you will need to make,  but ways of automating some of the care, as well as the kind of plants you grow,  will all influence the amount of ongoing labor that will be involved in your unit. But before we get to that, let’s back up and look at the overall picture.

The Greenhouse Idea - Planting the Seed

If the idea of a greenhouse appeals to you, then taking inventory of your lifestyle and available time is a good place to begin. Do you have time each day to relax as you care for your greenhouse? How much time do you realistically have available? Do you travel out of town overnight frequently or for extended periods of time? If you do, do you have someone in the family, or a friend, who will care for the greenhouse and plants while you are gone? Remember, the greenhouse and plants do not go on hold while you’re gone! There are automated systems that can be put in place, but a human is usually needed to oversee the goings-on. If your time is limited or you travel frequently, you might want to focus on a downsize greenhouse and a growing system that will require no more than a couple hours a day.

You can really dream and get creative as you plan! Greenhouse growing can be a fun and fruitful family activity, or a great way for friends to socialize and relax together. As you plan your greenhouse, you may want to allow enough room for yourself and another person or two. Some folks like to include enough room to set up a table and chairs where they can enjoy a cup of tea or coffee. Others like some patio chairs to relax and read in, still others like to set up a pond or even a small waterfall to enhance their daily greenhouse experience. Of course, this means leaving some open space in your greenhouse so that you can set up the extras that will help you enjoy the special environment you are maintaining.  Taking relaxation one step further, some folks even install a hot tub in the greenhouse! On a more practical note, you may want to incorporate a workbench and a sink with a drain. Already, this little greenhouse you initially thought about needs to be bigger! Make a list of what you want to do in your greenhouse. Have a brainstorming session and have a friend or two look at the list and see if other possibilities arise.

Dealing with Specifics and Planning Ahead

When your list is finished, you might discover that your list is longer than what your budget will conveniently accommodate. If that is the case, you’re going to need to do some trimming.  Keep in mind the most important rule of thumb: it is easier to add internal features to the greenhouse over time, than to add space to the greenhouse once it is in place. As an example, the environmental control system in a greenhouse is generally designed specifically for that size unit. As a result, making the greenhouse larger after it is first built makes the original environmental equipment obsolete because of its lack of increased capacity.  Many people also find that the greenhouse they planned isn’t large enough once it’s erected and they have filled it and are using it. Both hobby greenhouse owners as well as commercial greenhouse growers complain that they didn’t start with a big enough greenhouse. So be sure to make the basic greenhouse larger than you think you’ll want if you can in any way work it into the budget.

Now, let’s move on to planning the location to erect the greenhouse. A suitable greenhouse location will include a spot where the sun reaches most of the day. An open spot is needed where the sky is clearly visible to the east, south and west if you’re in the Northern Hemisphere. If you’re in the Southern Hemisphere, you want the northern sky rather than the southern sky. Anything short of this will reduce the maximum plant growth in your greenhouse. A little shade is tolerable because you’re not building your backyard greenhouse to maximize commercial production. But you need enough light to have a reasonable level of success.

The greenhouse should be level from side to side, so a level site is needed. You need to create a natural flow for drainage within the greenhouse. To achieve this, the floor should be sloped at least 1% toward the winter sun end of the building.  This slight slope is not noticeable as you move around the greenhouse, but it will facilitate the drainage of many of the plant production kits that you may later decide to install.

Yet another factor in determining the location of your greenhouse is access to the utilities you will need - electricity, water and fuel to operate the environmental management equipment and to feed the plants. Generally speaking, the farther away from your residence the greenhouse is located the more it will cost to run those utilities to the site. If you want or need to run any drainage from the greenhouse into the residential sewage system, the location of the greenhouse will impact the cost of the line, as well.

To avoid unnecessary costs in the future, plan ahead so that you need to run the utilities to the site only once. Just like when you plan the size of the greenhouse, it is best to size things beyond what you think you will need. Over-size things to at least half again what you anticipate needing as long as doing it doesn’t cost more than twice as much. As you use your greenhouse, you’ll inevitably come up with some new ideas and projects you will want to try in your greenhouse. If you’ve planned ahead and installed utilities that allow for growth, incorporating those ideas will be a lot more doable and less expensive.

As an example, if you think you may someday want to run artificial lighting (high intensity discharge lighting) in your greenhouse, it makes sense to run a big enough electrical service to the greenhouse when you first install the utilities to handle the future need. Supplemental light uses a lot of electricity! If you are preparing for the possibility of lights, consider supplying enough power to your greenhouse to run 16 to 17 watts per square foot (or160 to 175 watts per square meter) of greenhouse area.

Water is a critical component in greenhouse growing. The water quality is going to be very important to the plants in the greenhouse. You should have the water tested before you decide to put in a greenhouse. Most water can be used, and possible shortcomings in water composition can often be managed. But if your water needs some treatment to be useable, or is not useable at all, that is something you need to know before you commit to your greenhouse project. Since an alternate source of water is usually not available, you’re going to need to take the steps necessary to make the water you have suitable for use. It could cost a few hundred to a few thousand dollars to treat the water to make it usable in the greenhouse. If you have a water softener in your home, do not use softened water in the greenhouse! Tap into the water line before it goes through the softener - directly from the unsoftened, incoming supply. The calcium and magnesium removed from the water by the water softener is good for the plants. The sodium introduced to the water, however, can only be tolerated up to a limit of about 75 parts per million (ppm).  In most water softener applications, the sodium in the softened water will be higher than 75 ppm or the water softener probably would not have been needed in the first place.

Yet another area to deal with as you plan your greenhouse is local zoning regulations.  In some areas, you will need to abide by zoning restrictions. Because zoning regulations vary widely from area to area we suggest you check with your local zoning authorities early in your planning.

Let’s move on. You’ve done the basics.  You know you have zoning approval, your water has been tested and it’s useable and you have the perfect spot for your greenhouse. How do you know which direction to orient the building?  The preferable orientation for the greenhouse is a north-south direction going along the length of the greenhouse. This is to maximize the amount of natural light received by the contents of the greenhouse throughout the year. Greenhouses built for bedding plants are often oriented the other way and many books will tell you to orient greenhouses the other way, but the North to South orientation is preferable to maximize light. You can vary that orientation up to 12 degrees to the east or west if that will help you line it up with other things on your property. That amount of deviation will not significantly affect light exposure and the productivity of the greenhouse.

So much for the technical and the planning. Now, on to the rewards... the time spent in the greenhouse will include culturing, watering and caring for plants. It will also be a time away from the cares and demands of the rest of your life. The environment in the greenhouse can provide some quietness and calm in the midst of our fast paced, stressful lifestyles.

Plants are dependent upon us, but they also give to us. Meeting their simple needs is usually fulfilling rather than a hassle to us. Beauty to the eye, and delicious, fresh edible parts are just some of the rewards that plants share with us.

Plant care has so many beneficial effects for humans that Horticultural Therapy is an entire discipline. It is well known that having people with certain problems work with and care for plants has beneficial influences for them. Benefits from caring for plants can be enjoyed by the rest of us also.

Nuts and Bolts

The most obvious part of the greenhouse environment is the structure. It is the necessary packaging that provides light penetration at the same time that it provides isolation from the outside elements. Environmental controls and feeding systems are what make the enjoyable atmosphere when we’re in our greenhouses, plus they keep the plants growing even in our absence. Heaters, fans, evaporative coolers, feed systems and environmental controllers are all system components that are important. Together, they can cost more than the greenhouse structure itself. Some greenhouse purchasers have the unfortunate experience of purchasing the structure, then discovering that they need far more in order to make the greenhouse work. For this reason, you should take a systems approach when planning and buying a greenhouse. Make sure all the ancillary equipment you need, like environmental control hardware, is included in your greenhouse purchase. Pay attention to the actual components of your structure, from bottom to top.

Even the structure itself needs some attention in the planning stages. The quality of the structural components will determine how well and how long the greenhouse will stand. Light weight aluminium, pvc plastic and fence-grade steel are sometimes used as greenhouse structural components. Structural steel will perform better and last longer. It may cost a little bit more than some of the alternatives, but it will outlast them and be more cost-effective in the
long run.

Greenhouse coverings run the gamut from glass to polycarbonate to greenhouse polyethylene (heavy plastic sheeting). Glass and tempered glass greenhouses are the most expensive structures. Except for possible breakage, the cover will probably never need to be replaced. Double walled polycarbonate has a 12 to 15 year life. A double walled polyethylene greenhouse with an air space between the two poly layers is a relatively inexpensive cover with a limited life of an average of four years. Your budget, aesthetic considerations and possibly zoning restrictions will be considerations when making choices in this area.

Heat, Cold and Ventilation

Do you really need to put a heater into your hobby greenhouse? In most parts of the world, the answer is yes if the greenhouse is to be run and enjoyed all year. There’s not much insulation value in the covering material of the greenhouse – this is partly because the materials used must be designed to allow transfer of light into the greenhouse.  Even when days are warm enough for people to enjoy the greenhouse environment, the nights may be cool enough that the plants would suffer or be damaged without a heater.

Air movement through the greenhouse is necessary for the proper growth of the plants. Air movement is used to provide cooling of the greenhouse environment. A system of vents can be used for greenhouse cooling, such as what are found in a naturally ventilated greenhouse, which is designed so that the placement of the vents will work to move air through the greenhouse. Air currents outside of the greenhouse greatly increase the airflow within the greenhouse. When greenhouse cooling is needed, how often is there air movement outside the greenhouse to help facilitate the inside cooling? In different parts of the world, the answer to this question can vary considerably. If there is good natural air movement in your area, does it occur in your back yard? Are there structures or trees that block or reduce air movement in the area of your greenhouse? If you use natural ventilation in your greenhouse, should you have manually operated vents or power vents? That depends upon whether you can be present in your greenhouse whenever the vents need to be adjusted. For most people, that means that power vents are the answer.   However, natural venting, while less expensive, is not always the most consistent means of temperature control within the greenhouse, especially in locations where air currents are erratic.

The most consistent way to cool a greenhouse is with electrical exhaust fans and louvers or an evaporative cooler. The rate of air movement through the greenhouse is more directly controlled by the operation of the fan(s). This way, when outside air is still, greenhouse air movement can still be generated by the operation of the greenhouse fans.

An evaporative cooler can provide air into the greenhouse that is cooler than outside air. This is equipment that may be added to a greenhouse later if the initial costs get beyond the budget.  Even if installation will take place in the future, it’s best to plan for it from the beginning so that the proper control equipment, utilities and space are already in place when it is added.

Evaporative coolers can more effectively reduce the temperatures in areas where the average relative humidity is lower than in areas of high relative humidity. Generally speaking, temperatures are higher in areas of low relative humidity than in areas of higher relative humidity. An example of this is the difference between the summer desert (low humidity/high temperatures) versus the high humidity but lower summer temperatures among the Great Lakes region.  In areas where the evaporative cooler will lower the temperature five to seven degrees °F (three to four degrees C), that temperature reduction can keep the plants healthy for a significant additional time. In many areas of the world, some form of cooling is necessary if the greenhouse is to be operated year round. An evaporative cooling system will provide the most economical cooling in most applications. A more effective, but more expensive mist system is available but likely to be reserved for commercial growing in naturally ventilated greenhouses.

Environment control equipment costs can (and usually do) present  a higher percentage of the overall cost of a small greenhouse system, as opposed to the percentage of the overall cost it can present in a larger greenhouse system. The equipment is essential for creating and maintaining the environment necessary for plant health. Once again, when the whole system – both the structure and the necessary components - is considered in one package, the overall size can be adjusted to the budget, yet yield a fully functional greenhouse. If a person gets just a greenhouse frame without the needed environmental equipment, he or she might find that installing the needed equipment is out of the current budget and more expensive than it would have been as part of a complete package. Remember, the whole idea of the greenhouse is to provide a stress free sanctuary where you can enjoy your horticultural hobby, not another source of stress! Planning wisely is the way to accomplish this.

Do You Have to Use Soil?

The answer is no. Of course, we all know that plants can grow in soil.  But soilless plant growth can actually help avoid some difficult growing problems. Soilless greenhouse production developed when the use of soil treatment chemicals was banned and the cost of steaming the soil to prepare it became cost prohibitive. In a small system, soilless production is relatively easy and not expensive. Soil borne insects and diseases are not introduced to the greenhouse when sterile, soilless media are used.

If you need to start one step at a time, and can’t include the cost of a hydroponic or soilless system in your initial greenhouse investment, you can grow greenhouse plants in the ground during the first couple of years, assuming the soil is suitable for plant cultivation. Even if cost is not a factor, some people feel more comfortable growing in soil at the beginning of their greenhouse experience. (However, if your soil is not plant-friendly, then soilless media should be used.) After a few years, a combination of problems associated with the continual reuse of soil will usually encourage a transition to hydroponics or container organic systems.

Hydroponic production systems operate with the needed fertilizer ingredients dissolved in the water of the system. The fertilizer ingredients do not actively interact with the media in a purely hydroponic system. The media simply acts as a sponge for the fertilizer-rich water in the system, making the nutrients available to the plants.

Organic production systems involve microbial activity in the media. The microbes get their energy from the media and break it and supplied fertilizer sources down to simpler forms that can be absorbed by plants.

Although organic production can be done in the soil of the greenhouse, most people will find it easier to start with an organic soilless media mix. Organic fertilizer programs and supplies are available for these systems.

Several hobby production system kits are available for use in small greenhouses. You will probably want to choose one or more of them to produce a variety of plant types in your greenhouse. If the budget is tight by the time you reach this stage, you may want to get one or two systems and put off purchasing others until more funds are available. The systems are easy to add as you go along.

Small plants that reach maturity or harvest stage within a few weeks can be grown in an NFT (Nutrient Film Technique) system. Larger plants and plants that will be grown, cut and let re-grow will do better in the long run if they are grown in a media-based system. That media can range from an organic soilless mix to rockwool slabs to perlite in many types of containers or packaging.

You Did It Your Way!

Whether it’s flowers, bushes, trees, fruits, or vegetables, having your greenhouse and selecting your growing systems means that you grow things your own way. You experience the process. You’re part of the process. When doing this on a small scale, the entire growing experience need not consume more of your time than you can afford to give it. As you look around the plants thriving under your care, you feel you accomplished something and you enjoyed the path as you make the accomplishment.

Perhaps your goal is to grow plants for aesthetic enjoyment.  Grow what you like, surprise yourself with new varieties, with colorful blooms in the off-season, and with mastering plant propagation and other techniques you may have wanted to explore. Perhaps you like the idea of growing your own food. This way you know it’s safe, because you know how it has been grown and what has and has not been used to grow it. Of course, taking this on this type of growing will involve some commitment of time and planning a production schedule. Producing your own fresh food during the winter or in some areas during a stretch of hot weather can be challenging. An overlapping schedule for long term plants like tomatoes and cucumbers will need to be planned.

Whatever you want to grow and however you grow it – if you plan and choose carefully, you will be sure to have a pleasant experience. The tips and information reviewed in this article are provided to help get you started in the selection process with a minimum of surprises and hopefully no  disappointments. Check out suppliers carefully, make sure they have experience in a variety of systems and can discuss alternatives with you intelligently. Buy the best greenhouse structure you can, ask questions and invest now in what you can’t change later on – the size of your greenhouse structure, the quality and the basics.  The rest are fun things to add as you grow in experience as you enjoy tending to your plants. Happy growing!

Changes in seasons bring about changes in the external and internal environments of the greenhouse. These changes compel the grower to view things inside and outside the greenhouse differently. Although the idea is to attempt to keep the environment inside the greenhouse uniform, the way to accomplish this will change from one season to the next. Things that were previously outside may suddenly want to migrate indoors. You or your friends may even want to move some outside plants into the greenhouse.

Although the goal is to keep the environment in the greenhouse so that the plants are comfortable, have the things they need and are able to grow, the way it is done and the extent to which the goal is achieved will change with different seasons and outside environmental conditions. As the outside temperature increases to the plant comfort range, more air is moved through the greenhouse for cooling. Fungus spores and small insects can ride along with the air being drawn into the greenhouse. However, they all don’t ride out of the greenhouse with the out-going air. Some stay and set up housekeeping at the expense of your plants – and you.

Some summer outside dwellers look for a warmer environment for the late fall, winter and early spring. Rodents, like mice, are among such creatures. In different areas there will be different potential intruders. Major crops in some areas are harvested during a short period of time. This can leave large insect populations without lunch on very short notice. Your greenhouse could be one of the few locations providing the viable green plants they seek. Some of those many insects may find your greenhouse and like it, electing to stay. Keeping them out may be a challenge that requires extra preventative measures.

Prevention Through Exclusion

The first objective with respect to hobby greenhouse problems is to keep problematic creatures out of the greenhouse to begin with. It makes sense to go to great lengths to keep pests and problems out of a hobby greenhouse – it can be very expensive to clean up or eliminate a problem once it has become established!

An area covered with fine insect screen just outside the air intake is one measure to consider. In most locations, it should be a screen fine enough to keep out Thrips. Because such a fine screen will restrict air flow, the screen area should be at least five times the area of the greenhouse air intake (see photo). Often this is accomplished by extending the greenhouse structure with a section that is covered with the screening material. Plastic sheeting can be installed over top of the screening material in the winter in regions where snow may accumulate on any horizontal part of the screened area. Unfortunately, screening does not keep everything out forever. However, it can – and usually does – slow things down enough to make it worth the investment.

Screening one end while at the same time letting in anything and everything as you open and close the front door doesn’t make much sense. If you really don’t think about what you’re doing, that is exactly what can happen. Some suggestions on how to avoid this, accompanied with the reasoning behind the suggestion, will be given below. Some may be harder than others to follow.

We suggest that you start all your plants from seed in your own greenhouse. By doing this, you will greatly minimize the chances of introducing unwanted organisms to your greenhouse environment. Realistically, though, starting all your own plants doesn’t always work. Some plants grown from seed don’t come true to type, and are typically reproduced vegetatively. When the plants you plan to grow are vegetatively reproduced plants, the use of stock that has been reproduced by tissue culture is one of the best ways to minimize the chances of introducing unwanted things to your greenhouse. Plants started by tissue culture are going to be more expensive than comparable plants started by more conventional vegetative reproduction techniques. The extra cost, however, will be small compared to the cost of treating an entire greenhouse for imported problems. Often tissue culture produced plants are not as readily available as conventionally propagated plants. They may need to be ordered through specialty sources and are less likely to be available for impulse purchases.

Next, the media used for seed germination and the media used for plant growth should be commercially available, soilless media. This would include perlite, rockwool, and various soilless mixes. The purpose for this is to exclude insect and microbial pests that can live in soil. Although soil can be treated with either heat or chemicals to kill any undesirable inhabitants, many would consider either type of treatment environmentally unfriendly. For example, heat treatment kills at least some of the beneficial organisms in the soil, and it can also oxidize some of the soil organic matter.

Plants from outside should not be allowed to over winter in the greenhouse. They can bring in unwanted pests with them. Many greenhouse owners have given refuge to plants without realizing the possibility that they were introducing problems as they brought in their plants. Others have the thought occur to them a day or so later, sometimes spurred by the first evidence that a problem has appeared. You need to establish a policy regarding this in advance of the season when plants need to be brought in. Often, friends will request refuge in your greenhouse for a favorite plant or two. Having an answer ready for them – along with its reason – can save you from costly greenhouse problems.

Pets like dogs and cats are factors in potential greenhouse problems. This may well be a touchy area for some pet-owning greenhouse growers. The intention of the following advice is to help you minimize or eliminate the introduction of pests to the greenhouse environment. Not all pets need to be excluded from the greenhouse.

Outside dogs should not be allowed into the greenhouse any more than they would be let into your dwelling. There are too many things they could carry into the greenhouse. House dogs that romp through the yard, garden and adjacent fields on the way to the greenhouse should not be allowed into the greenhouse. Lap dogs, dogs that are carried or follow you on the path to the greenhouse are unlikely to introduce anything harmful to the greenhouse environment.

Cats are another consideration. There are different opinions about letting cats into the greenhouse. If the cat spends much of its time roaming around outside, it should stay out of the greenhouse. If it is primarily a house cat, there is less concern about letting it into the greenhouse. Some people, including some commercial greenhouse growers, have a greenhouse cat. The cat lives in the greenhouse. That is where it is fed and has its litter box. A greenhouse cat who is a good hunter can help with greenhouse rodent control!

Sometimes insects, mites or diseases can be taken into the greenhouse on materials or items that have been exposed to plants or produce in the grocery store. Used produce shipping boxes and plant shipping boxes should never be taken into the greenhouse. Even boxes that you have used to deliver your own greenhouse products should never be taken back into your greenhouse. They may have been exposed to other plants or infested produce in a storage area in the store. They could have picked up a disease or mites that would then be introduced to your greenhouse environment.

Even you and your visitors could introduce problem instigators into the greenhouse! You and they should not enter the greenhouse after being in another greenhouse, a garden or an agricultural field. Even visiting your greenhouse after preparing vegetables for a meal in your kitchen could introduce a problem to your greenhouse. Washing your hands before going to the greenhouse should be considered standard procedure after working with any plant or produce in the house or on your job. In fact, depending on the extent of the potential contamination to which you’ve been exposed, it’s advisable to do anything from washing your hands to changing your clothing, including your footwear, before entering your greenhouse.

Some greenhouse operators, including some of the big commercial growers, have a foot bath through which people entering the greenhouse step. However, most solutions that can be used in such foot baths are unstable and break down within minutes. A foot bath with a three-day-old solution gives no physical protection to your greenhouse.

Plant Diseases

Plants have natural resistance to many diseases. Some of those resistances are inherent within the plant while others are provided to the plant through symbiotic relationships between the plant and a microorganism. The microorganism is usually a fungus and it usually lives within the soil. Microorganisms can be introduced into the soilless production system and are used to help in disease prevention and elimination within the greenhouse.

Plant diseases result from the intrusion of one of three main types of organisms. Although there are a few instances where the causal agent is not within the three categories, most diseases encountered by the hobbyist will be caused by an organism fitting into one of the three categories. Physiological and even nutritional problems can be thought by the inexperienced to be a disease.

Most disease-causing organisms can be classified within the fungus, bacterial or viral categories. There are some generalities and similarities within each area. We will look at some of these in general terms.

Fungus diseases are typically spread by spores. A fungus spore is usually a reproductive body featuring a relatively small size and the capability of getting the fungus started in a new location. It is often very readily spread by moving air or within flowing or splashing water.

It’s fairly simple to minimize the possibility of water-borne spores in the greenhouse by using municipal water or well water. River water, pond water or reservoir water is more likely to carry water borne fungus spores. Municipal water from such sources is usually treated, so plant disease spores do not survive. If you use untreated water from rivers, ponds or reservoirs, you could introduce water borne fungus spores to your greenhouse. Such incoming water can be processed with ultra violet light water treatment systems to eliminate the risk of the introduction of fungus spores.

Air is blowing or being drawn through the greenhouse on a frequent basis during the warm months of the year. During these times, it is impractical to expect to exclude all airborne fungal spores from the greenhouse. The more realistic approach is to take steps to interfere with spore growth and development and its intrusion into the plants. This is achieved through environmental management.

Most airborne plant fungus spores need free water on the plant leaves or at least very high relative humidity in order to germinate and have a chance to gain entry to the plant. If high relative humidity could be avoided in the greenhouse, there would be virtually no fungus disease problems. In desert areas there are few or no problems with fungus diseases because the relative humidity can be kept down all times of the day for at least most of the year.

Most air borne fungus spores need several hours of free water on the plant leaves before they can germinate and gain entry to the leaf tissue. When the day temperature of the greenhouse is allowed to drop a few degrees to the night temperature, the dew point may be reached. At dew point, the air has more water than it can hold at the new, lower temperature. The water condenses out of the air on cool surfaces in the greenhouse, including the plant leaves and stems. Suddenly, the formerly dry plant now has an ideal environment for the fungus spores that have landed on it. The spores take advantage of the conditions and germinate. If the leaf remains wet long enough, the growing fungus will find a stomata or a small wound in the leaf where it will be able to enter the plant. If the growing fungus gets inside the leaf before the leaf dries off and the fungus dries out, the disease is then established in the leaf.

Some oxidizers, like hydrogen peroxide-based fungicides, can kill spores on the leaves before they germinate. Most conventional fungicides kill germinated spores before they gain entry to the plant. That, at least, is the objective. Once the fungus has gained entry into the plant, the process of eliminating it becomes a very complex and involved battle.

Bacterial Diseases

Plant diseases caused by bacteria are less common in the greenhouse than those caused by fungi. Bacteria are generally spread by contact. Therefore, a bacteria that gets into the greenhouse rides in on plant material or possibly people or pets.

Starting plants in the greenhouse from seeds, where practical, is a good way to minimize the possibility of bacterial diseases in the greenhouse. Established plants, bedding plants and cuttings can transmit bacterial diseases.

Some bacterial diseases are seed-borne. They can live on or in the seed while it is being stored. Most seeds are treated so that any bacterial disease that could be spread by the seed is very unlikely to survive. Most commercial seed producers are very careful not to use seeds from plants having a bacterial disease. The use of untreated seeds is becoming more popular as the organic trend continues to grow in popularity. Organic growers often require untreated or organically grown seed. These seeds could be more likely to carry a seed-borne bacterial or fungal disease.

Virus Diseases

A virus disease in the greenhouse can be the most damaging type of plant disease. Once it gets into a plant, a virus continues to grow and spread within the plant as it grows. Cuttings or any vegetative starts taken from a virus-infected plant will be infected. In some instances, tissue culture can be used to produce virus-free plants from virus-infected plants, but details on that are for a more in-depth discussion on tissue culture.

Virus diseases are spread in one of two primary ways. Some viruses, like Tobacco Mosaic Virus, are spread by contact. By working with or handling infected plant material, the virus can get onto your hands or tools and be spread to uninfected plants in a different location. Some viruses will remain viable on uninfected surfaces for hours, days or even months before being transmitted to other plants. You can spread Tobacco Mosaic Virus to plants in your greenhouse if you have handled infected tobacco, potatoes, peppers or eggplant. Wash your hands with Lava brand soap after handling any of the plant parts of the above plants and before handling tomato or petunia plants in your greenhouse to minimize the chances of transmitting the virus.

Once a virus that can be spread by contact has been introduced to the greenhouse, it can then be spread to susceptible plants in the greenhouse through your cultural work and handling of the plants. This often occurs before the first symptoms of the virus are visible and identified in the greenhouse.

Insect vectored viruses are the other type of virus that can be introduced to the greenhouse. This type of virus is spread through the feeding activity of insects like thrips or aphids. Each virus has its vector insect. Often, by the time the virus disease is noticed in the greenhouse, it has spread to several or all susceptible plants. Fortunately, these types of viruses are not widespread, common problems. If you are in an area where one or more of these viruses can be a problem, the best thing to do is to keep the insects out of the greenhouse as was discussed early on in this article.

Using Beneficials in the Greenhouse

Many of the common insect and mite problems in the greenhouse can be controlled with the use of general or specific beneficials. Beneficials can be defined as insects or mites that live on the insects or mites found on the plants in the greenhouse. Many commercial growers use beneficials. A large part of the cost of using beneficials, even for the commercial grower who buys in large quantities, is the shipping. A small grower may need fewer beneficials, but the shipping costs are going to be the same.

There are two overall types of beneficials based on how they are used. There are general purpose beneficials like lacewings. Although lacewings prefer aphids, they will find something else to live on if no aphids are present. They will survive and be ready to welcome any aphids that might find their way into the greenhouse. Beneficials like this can be introduced on a somewhat preventative basis, but may need to be introduced on an ongoing basis because the numbers will not be maintained when their favored food source is not present.

Other beneficials are very specific in what they will control. Some of the small wasps that are used as beneficials paricitize the pest and spend part of their life cycle within the pest. The pest is killed in the process. The beneficials that operate in this manner are very host-specific. If their host is not present in the greenhouse, the beneficial will die without reproducing. Use of such beneficials in a small greenhouse on a preventative basis is not considered a good approach from an economic standpoint.

The hobby greenhouse can bring many hours of enjoyment and much in the way of produce, but this does not come without some challenges. With adjustment in your approach and understanding the needs of your greenhouse during seasonal changes, the challenges will be manageable, and most problems avoidable.

A little knowledge about what to do – and not do – will arm you for success and bring many years of
happy growing!

Summer – at least not natural summertime – is typically not the season for which most people purchase their greenhouses. The idea of a greenhouse is to create summertime in the greenhouse when the climate is something other than summer-like outside. During summer months, however, most greenhouse gardeners want to keep things going in the greenhouse so that they do not have to start over again when autumn arrives and it is time to get things going again in the greenhouse.

Several factors need to be considered in the overall plan when setting the greenhouse up to include summer operation. Cooling equipment, control equipment and enough of the grower’s attention are all required for the greenhouse and its contents to make it through the summer.

Greenhouse Cooling Equipment

Summer temperatures are not only warm enough outside the greenhouse for your outdoor plants, but they make the greenhouse environment even warmer. Heat accumulates in the greenhouse both when it is cool outside and also when it is warm out. Often in the summer the heat will accumulate above desired levels in the greenhouse unless we take preventative measures. Simply bringing in outside air will cool the greenhouse to some degree during the day.

Greenhouses are built to be cooled in one of two main ways. The cooling method chosen affects the design of the greenhouse from the beginning. A naturally ventilated greenhouse is equipped with shutters to allow for the exchange of the warm inside air for cooler outside air. Taller, naturally ventilated greenhouses work better than those not so tall. The location of the greenhouse in respect to other buildings or tall plants and the direction of the prevailing wind can have an influence on the proper operation of the natural ventilation system. Hobby greenhouses are not always located in ideal locations for optimal operation, in terms of air current and other factors. A fan- and pad-cooled greenhouse makes use of electrically operated fans to force the air exchange. Sometimes just shutters (no cooling pads) are used to allow air to enter the end of the greenhouse opposite the exhaust fans. This type of system is not really designed for operation during the hot summer months in most areas.  Some growers in far northern regions or at higher elevations may be able to adequately operate a greenhouse without cooling pads.

The use of the evaporative pads provides for the introduction of air to the greenhouse that is cooler than the air outside the greenhouse. The water that is introduced to the evaporative pad cools the air as it evaporates into the air moving into the greenhouse through the pad. The lower the initial Relative Humidity in the incoming air, the greater the cooling potential of the system. Even in higher Relative Humidity situations, at least three to five degrees of cooling are usually achievable.

Cooling System Controls

Control systems are needed for operating either the naturally ventilated or the fan and pad cooling system. Although it may be claimed that either system could be operated by hand, manual operation would tie the operator to the greenhouse system and require more time and attention than most hobbyists can afford.

Either a thermostat-triggered system or a programmable environmental control system will provide the automatic control needed to operate the environmental modification equipment when it is required to make the desired change in the greenhouse environment.  Beyond the convenience of automatic operation, programmable environmental control systems will give more extensive and more accurate control than will the use of thermostats alone. In other words, the environmental conditions within the greenhouse can be kept closer to the desired target conditions more of the time with a programmable control system than with a thermostat-based system. The programmable environmental control system, however, is probably at least four times more expensive as the system operated by thermostats.

The vents in a naturally-ventilated greenhouse would need to be motorized in order to be controlled by either thermostats or an environmental control system.  Motorized vents cost quite a bit more than vents without motors.

Greenhouse Shading

Even with several stages of greenhouse cooling, the greenhouse and its plants can get too warm at times. Greenhouse shading is a last-resort cooling measure.

The material used to shade the greenhouse can be shade paint, shade material or a movable shade curtain. Shade paint is the cheapest alternative. Its use involves the brush, roller or spray application of the material to the outside of the greenhouse. Because of the nature of the shade paint and the texture of the greenhouse cover, the finished job looks like a very sloppy paint job no matter how carefully or uniformly it is applied. Many hobby growers (and their neighbors) prefer a more attractive method of shading the greenhouse.

A coarse fabric shade material can be applied over the top of the greenhouse and tied down. Materials are available in different colors and densities. Because white shade material gives more cooling for the light it cuts out, it is used over greenhouse covers rather than the cheaper black or green material frequently used for commercial shade house set-ups. The white shade material is usually installed in the spring when the temperatures inside the greenhouse would rise above the maximum desired temperature without some type of shade. It is removed in the fall when cool enough temperatures can be maintained in the greenhouse without its use. Some growers will take the shade material off the greenhouse or slide it to the north end when the weather is expected to be cloudy for several days in a row. This way, the shade material does not interfere with the light getting into the greenhouse when it is in limited supply.

Motorized movable shade curtains inside the greenhouse are sometimes used in large, expensive commercial installations. Because they are the most expensive technique for shading, they are not often used in hobby greenhouses. The system would need to be planned for when the greenhouse is being installed. The structural design of the greenhouse must be planned to accommodate the shade curtain. It is not something that can be added to just any greenhouse.

Environmental Shading

A hobby greenhouse is usually not the first object to be located in your back yard. Because of the light needed to do a good job growing in the greenhouse, the location of the greenhouse needs to be carefully considered. Tall plants and buildings, including your residence, should be located so that they cast as little shadow as possible on the greenhouse.

The most valuable light for the plants in the greenhouse is the light from the east. The morning light will usually come at cooler temperatures than light later in the day. Plants will make the best use of the light they receive earlier in the day. When surrounding objects will cast natural shadow over the greenhouse sometime during the day, it is best to locate the greenhouse so that the minimum shade is received by it in the morning, maximizing the greenhouse’s exposure to morning light.

Afternoon shading of the greenhouse by plants or structures can help keep the temperature down in the greenhouse during the latter part of the day, although this is not the best way to shade and cool the greenhouse. However, if the greenhouse must be erected among objects that will cast shadow upon it, the location of the greenhouse should be planned so that the shade occurs at the best possible time for the plants to be grown. Similarly, when the removal or trimming of some of the surrounding trees is being planned, the effect of this on the shading of the greenhouse needs to be considered.

Shading material should not be used on areas of the greenhouse where the shade from other buildings or plants will naturally occur. Shadows move as the sun and earth change positions throughout the season. You might need to observe and make adjustments as shadows on the greenhouse progress along the greenhouse surface throughout the seasons.

Your Personal Summer Schedule

Generally speaking, people tend to wander farther away form home for longer periods of time during the summer. A greenhouse, especially a greenhouse that may get too warm, can not be left unattended for very long. Someone needs to be available to make sure things are operating the way they need to operate. Ideally, that person should be outside the immediate family because things like vacation outings often include everyone in the family. The temporary greenhouse tender will need to be trained ahead of time. That will involve a time commitment over a period of time. It usually requires a level of interest on the greenhouse tender’s part.

It’s important to arm your fill-in greenhouse tender with all the information he or she will need to do the job. A clear understanding of what is to be done and contingency plans if something goes wrong need to be discussed, understood and outlined.  Plants in the greenhouse, unexpected expense and even a friendship may be in jeopardy if the possible scenarios are not realistically addressed.  Keep notes on what has gone off track on your own watch, and that will give you a background for training your stand-in person.

If possible, you should be accessible by telephone at least at certain times during your absence. This enables your stand-in to contact you if something outside the range of things discussed occurs, if there are questions, or if anything serious has occurred.

Making the Right Decisions When Planning Your Greenhouse

There are many choices that need to be made at the time you first plan and design your greenhouse. Some of these details and their importance are initially not understood by the inexperienced greenhouse purchaser, but speaking with an experienced, qualified professional and discussing all the options and considerations will help the grower make the right decisions at the outset.

The insects and mites that could become a problem in your greenhouse live on plants. If you bring plants into your greenhouse from a friend’s greenhouse or even your own yard, the pests could travel along with them. It is difficult to impossible to make sure there are no hitchhikers on plants that you bring in.

Even if you buy plants at a nursery or a garden center, you can not be assured that the plants are perfectly clean. Some vendors will be better than others. If you have been getting plants from a good producer and have not had problems in the past, it would be a good idea to stick with that supplier even if the prices are higher.

Another step you can take is to change the sequence of your gardening habits. Insects and mites can ride along on you. Go to your greenhouse before rather than after you work in your outside garden. The same holds true if you visit a friend’s garden or greenhouse. If you’ve been out and about where there have been plants, you do not want to go into your greenhouse before changing your clothing and brushing your hair. Even if you are out for a walk in the woods, you should clean yourself up and change your clothing before going into your greenhouse. Insects are notorious hitchikers

A dog may be man’s best friend, but it is not your greenhouse’s best friend. There is probably no problem in carrying a lap dog out to the greenhouse directly from the house, but a dog that takes a detour through your garden and a field or two on its way to the greenhouse, or a dog that lives outside should not be allowed into the greenhouse. It’s likely to bring insects or mites into the greenhouse with it.

Screening the air intakes of the greenhouse will help keep insects and mites out. A very fine screen like a thrips screen will keep almost any insect or mite out. However, it will also restrict airflow through the greenhouse. For this reason, it is necessary to build a box to increase the surface area through which the air can be drawn by the greenhouse equipment. The air intake surface area for a Thrips screen should be five times the unobstructed air intake area. This allows for the collection of a little dust on the screen, but the screen should be cleaned periodically to prevent the build-up of dust and flying plant seeds which obstruct the air flow. Installing a door in the screen box is helpful, enabling you to go inside and hose down the screen from the inside to clean off accumulated dust and seeds.

A double entry way for the greenhouse should be used if insect screening is used on the air intakes. This prevents the wind from blowing into the greenhouse when you enter, and for pests to gain entry. When using a double entry, make sure one door is closed before the other one is opened. Some people even look around to see if anything came in with them before proceeding into the greenhouse. This can become a consistent habit, but can become a challenge when a group of three or four people is going into the greenhouse simultaneously. Usually, some done will be polite enough to hold both doors open for others. Unfortunately, this allows the insects to gain entry into the greenhouse along with the people.

Plant beds, potted plants and weeds outside the greenhouse should be eliminated. Any plant material near the greenhouse - especially near the greenhouse door - can serve as a reservoir of pests waiting for an opportunity to enter.

Common Insects and Mites in the Greenhouse

Some insects and mites are more likely to set up residence within your greenhouse than others. Most insects and mites don’t bother us. It is just the few that do that give the whole group a bad name in many people’s opinion.

Before action is taken when an insect has been spotted in the greenhouse, some kind of identification should be made. The first thing that needs to be determined is whether the insect or mite is feeding on the plant. Insects like caterpillars chew holes in leaves. This is fairly obvious feeding activity. Insects like Thrips cut open a number of cells in a patch on a leaf and then drink the cell sap. They will often leave spots of excrement in the feeding patches. If you know what to look for, this type of damage is fairly easy to spot. Other insects and mites suck the juices out of the plant. Although this can not be easily detected once the insect or mite moves along, the insect or mite spends a fair amount of time boring in to the plant tissue and does not move on quickly. They are usually moving slowly enough that they can be observed. Some of us may need to use a magnifying glass to get a good look at these rather small insects or mites.

Caterpillars

Caterpillars are the larval stage of butterflies or moths. They hatch out in the greenhouse from eggs laid by their mothers, who flew or crawled into the greenhouse. If you keep the adults out of the greenhouse, there will be no eggs to produce the caterpillars. Moths and butterflies are fairly easy to keep out of the greenhouse with a little care, a double entry way and a fly swatter.

The Tomato Pinworm is one caterpillar that can become fairly well established in a greenhouse having several tomato plants. Unlike most caterpillars, this larva lives between the upper and lower leaf surfaces. This habit makes it very difficult to eliminate with conventional chemicals or biological stomach poisons. A firm squeeze of the leaf occupant will effectively stop the feeding and development of the caterpillar. In a small greenhouse, this will be effective if efforts are made to keep adults out and if the few caterpillars that develop from the eggs of adults that do get into the greenhouse are hunted down and squeezed. Some growers prefer to wear rubber gloves when doing this job.

Aphids

Aphids are sometimes referred to as plant lice because they suck the juices of the plant. They are fairly small and easily transported into the greenhouse on incoming plants or the clothing of people who have been around infected plants. Although most aphids are wingless, there is a winged stage that develops when the population gets crowded or in the fall, when the aphids spread. This is a much more mobile form of the aphid.

There are many different kinds and colors of aphids. What you may get in your greenhouse is determined to some extent by what kind of crops are being grown outside in your area and what kind of aphids feed on them. A major crop that is harvested and almost completely removed from the field in a short time period can leave many aphids without lunch. They will move around as much as they can while looking for a food source. Your chance of getting aphids into your greenhouse after an event like this in your area is great unless you take precautions like having a double entry way and having the air intakes screened as discussed earlier. A closer inspection of yourself and others entering the greenhouse is also in order when hungry aphids are looking for a living green spot in your neighborhood. Aphid populations can build very rapidly in a favorable environment, and a greenhouse environment is favorable to many aphids. Except for when they are preparing for over-wintering, aphids bear living young. To make matters worse, female aphids can do this on a repetitive basis without the participation of a male aphid. The offspring are female and can contribute to the population surge by producing their own young within a few days.

Once aphids are in the greenhouse, the use of insecticides will be necessary. Many insecticides are labeled for aphids. Some organic preparations are suggested for aphids. Several beneficials are also effective against aphids.

Whiteflies

Whiteflies love a greenhouse environment. Although they can fly, they are not strong fliers and don’t do well if there is much of a breeze let alone a wind. The greenhouse environment protects them against sudden strong air movements. When they fly, whiteflies form a zigzag flight pattern that runs for a short distance that is generally a maximum of three to five feet. They are well known by most commercial and hobby greenhouse growers.

The traditional Greenhouse Whitefly has been joined by additional types of whiteflies. The names include Sweet Potato Whitefly, Silver Winged Whitefly and Tobacco Whitefly. No attempt will be made here to distinguish between the whiteflies here. When, however, one of the other whiteflies comes in, it can drive the traditional Greenhouse Whitefly out. For a while, there can be a mixture of the whiteflies in the greenhouse. Eventually, however, the other whitefly wins out and the Greenhouse Whitefly disappears.

The Sweet Potato Whitefly, the Silver Winged Whitefly and the Tobacco Whitefly are all a little more difficult to control with chemicals and they require a different predator than that which will control the Greenhouse Whitefly.

It would be a good idea to get help identifying the kind of whitefly you have in the greenhouse when you detect a population starting. Check this each year, because the type of whitefly infesting the greenhouse can change from year to year in the same area.

Whitefly adults usually congregate at the top of plants. They lay their eggs on the bottom side of the upper plant leaves. The eggs hatch and go through three larval stages while on the bottom of the leaves. The last two larval stages settle down in one location and suck the juices from the leaf cells. This is followed by a pupal stage from which the new adult whitefly emerges. During the time this temperature dependent, 21 plus day process occurs, the plant continues to grow. Later stages of the life cycle are found lower on vertically growing plants.

Because of the life cycle of the whitefly, it is difficult to control. You may get all the adults but more may hatch out the following day. Even if there are no adult whiteflies on plants brought into the greenhouse, whitefly eggs or immatures may ride in on them. Yellow sticky cards are often used at the top of the plants as whitefly population monitors. They can also be used to help in the early detection of whitefly presence in the greenhouse.

Spider Mites

Spider Mites are very small mites that can be seen if you know what to look for and where to look. Even adult mites do not fly – they do not have wings. They are in the family of spiders and are not technically considered insects. Many insecticides, therefore, will not be effective. Miticides are used to kill Spider Mites.

Spider Mites prefer some plants over others. Cucumber and squash plants, for example, will be inhabited by Spider Mites before tomato plants located in the same greenhouse. However, if the cucumber or squash plants are removed, the Spider Mites will certainly move to the tomato plants rather than starving to death.

Feeding consists of the sucking of plant juices by the immature and mature Spider Mites. Often, Spider Mites will start on the underside of the leaves at the top of the plant. They prefer a dryer, warmer environment, and the top of the plant is usually dryer and warmer lower portions of the plant. Heavy feeding by large Spider Mite populations will give the leaf a speckled, yellowed out appearance. Closer examination, with a magnifying glass if needed, will reveal the Spider Mites.

Webbing that looks very much like spider webbing will be evident on severely infested plants. When the webbing appears, the Spider Mite population is very well established in the crop and greenhouse.

Spider mites can be present in outside gardens and crops. It is very easy to carry them from these locations into the greenhouse if precautions are not taken. Field crops like soybeans are very susceptible to Spider Mites.

Leaf Miners

Leaf Miners are a challenging pest. The adult looks like a small fly. Unless you have a background in Entomology, you probably will not identify the adults as a problem even if you see a few of them on your sticky yellow monitoring cards.

The adult Leaf Miner lays an egg on the leaf of the plant. The larvae tunnels and eats leaf tissue from between the upper and lower surfaces of the leaf. Once the larva is inside the leaf, it is protected against anything that would be sprayed on it. There are beneficial parasites that will control and eliminate Leaf Minors when properly introduced.

Leaf Miners usually pupate in the soil. If the larva drops onto a hard surface like a concrete floor, it will be killed and will not complete its life cycle. Hydroponic greenhouses having concrete floors are less likely to have Leaf Miner problems than greenhouses with other flooring surfaces.

Gnats

Gnats are usually more a nuisance than a real damaging problem in the greenhouse. Adults lay their eggs in the algae on the growing media or other lighted surface in the greenhouse. The larvae mainly live on dead organic matter. Once in a while, the larvae will nibble on a few young roots.

The adults make a nuisance of themselves by flying up into your face when they are disturbed and detract from your enjoyment of your plants by their presence on your plants.

Beneficial nematodes can be used to control Fungus Gnats. Some chemicals and natural products can also be used to control them. Because there are so many places in the greenhouses that gnats can breed, it is difficult to cover them all with a sprayed material.
Slugs

Slugs work the night shift. They’re neither insects or mites. They chew on the leaf tissue and leave holes in the leaves. They do this at night and then hide during the day, when it is very difficult to spot them. Many people think they have a mystery problem when they have slug damage. There are a few clues that can be identified. The droppings look very much like those of caterpillars.The slug trails, however, are the dead giveaway clue. Slugs will leave a narrow silvery trail where they have crawled. This sometimes can be seen on the plant stem and leaf where their feeding damage can be seen.

Find the slug’s hiding place in the greenhouse and eliminate it. Slugs will hide under loose dead leaves or under a piece of wood or other items lying on the ground or the floor of the greenhouse. They can sometimes get under plant pots and hide. Hunt them down and escort them out of the greenhouse

Controlling and Eliminating Pests

Preventing and eliminating pests in the greenhouse is an ongoing effort. Several preventative and control strategies need to be considered. Obviusly, if the pest is kept out of the greenhouse, we don’t have to get rid of it. The barriers, procedures and precautions mentioned earlier in this article need to be implemented to the fullest extent practical and possible. The potential for problems with pests will be reduced by these practices, but not eliminated. If it were that simple, you probably would not be reading this now.

Most pests have a life stage during which they are more vulnerable to control measures. The more you know about the pest and how it grows and reproduces, the better choice you will make when it comes to a control strategy.

At least once a week, take time to inspect the plants in the greenhouse for insect and disease presence or damage. Yellow sticky cards and other monitoring materials should be used as an aid in the early detection of insects in the greenhouse. Some creatures are attracted to the monitoring materials and some are not. You need to use both the monitoring materials and the visual examination of the plants to make an early diagnosis of a problem. The earlier a problem is detected, the earlier the treatment can be started and the smaller the problem will probably become. Beneficials – insects or mites which are natural predators or parasites of problem pests – are available for many of the insect and mite infestations that can occur in the greenhouse. Many commercial growers use beneficials on a regular basis. For a small or hobby grower, the cost of using beneficials can be quite high, relatively speaking, because the cost of using beneficials is mainly in the shipping cost. Although you will need a fraction of the number of beneficials that a commercial grower will need, the cost is going to be almost as much because the shipping charges are as much for a few as for five to 10 times as many beneficials. The effective use of beneficials usually involves three or more separate introductions of beneficials, which translates to three or more separate shipments. Most beneficials cannot be stored away for a week or so after they arrive. They need to be put out into the greenhouse where they do their work and get their lunch, in order to survive.

Conventional chemicals can be used against many of the insect and mite problems in the greenhouse. The number of these products currently on the market, as compared to a few years ago, has decreased. Some have been removed from the market due to chemical regulations and at the same time, fewer new products are being introduced. Many growers, however, choose not to use such products, preferring to grow in an environment without these substances. They may also want to eat produce they have grown that has not been treated with conventional pesticides.

Various other products can be used to control insects and mites. Some products are available that are approved for “organic” production. They offer at least some level of effectiveness. Sometimes, their mode of operation is as a discouragement rather than a killing action against the pest.

Don’t Get Bugged

The bottom line is that while the conscientious greenhouse grower will take every precaution practicable in preventing a pest infestation in his greenhouse, pests will still present a problem from time to time. The best solution is for the grower to arm himself with knowledge so he is ready to swiftly and effectively deal with pests when
they appear.

You’ve decided to take the plunge and purchase a hobby greenhouse. Once you’ve received and constructed it, it’s time to get it ready for plants and for making decisions on what you want to grow. It is likely that your list of plants to be grown and things to be done in the greenhouse can be unrealistically long. The information here is intended to help you take a realistic approach. There are many variables in what is realistic. These include the background and experience of the individual grower, the available time they have and what they expect from the project. The following guidelines and suggestions may help the new grower set realistic goals and expectations, which are more likely to result in a satisfying growing experience.

What is to Be Grown?

Once you have your greenhouse ready to provide the needed environment for the plants, the tendency is to overstock the greenhouse. This leads to tough discard decisions when the realization strikes that the greenhouse cannot hold every plant that has been produced. Young plants take up less room than they will need when they get older. If the greenhouse is filled with young plants, it will not be big enough for the plants when they get just a few weeks older.

Determine or find out the space needs of the plants when they reach the growth stage you expect to grow them to in the greenhouse. Calculate the greenhouse space you intend to allocate to that type of plant. Then determine how many of those specific plants you can grow in that space. You may find that you have some decisions to make at this point. Adjusting expectations, however, is usually less painful than disposing of plants that can no longer be accommodated by the available space in the greenhouse.

Overcrowding plants can lead to situations far worse than simple frustration as growers decide what to cull from the collection of plants. Plants will not grow and produce properly when they lack adequate space. They will compete for space and light, thus stretching and not concentrating their energy on flowering and fruiting. Plants stressed in this way are usually more susceptible to diseases and insect damage because crowded foliage provides an environment that protects them in their early development. Therefore, when you make the list of plants to grow in your hobby greenhouse, be realistic, do your homework on the space needs of each plant, and remember it is best to be conservative and add plants later on rather than eliminating plants in an overcrowded greenhouse.

Seeding Plants

Starting with seeds in the greenhouse is preferable to using cuttings or seedlings from another location. You are much less likely to introduce insect, mite or disease problems to your greenhouse if you start from seeds.

Seed 20 to 30 percent more seeds than the number of plants you want. Not all seeds will germinate all the time and not all the seeds that germinate will produce a strong, vigorous plant. This will mean that you will need to throw away some of the seedlings at transplant time. This is understandably tough for some beginning greenhouse growers. It is, however, the best way to establish a good, healthy plant population in your greenhouse.

What Plants Do You Seed?

The beginning grower needs to make decisions on the kind of plants they want to grow and the number of each of those different plants. Will they be ornamental or edible plants? It’s best to limit the diversity of plants at the beginning. As experience is gained and success is achieved, additional species can be added.

Unfortunately, most new hobby greenhouse growers don’t want to slow down and start at the beginning. They want to immediately achieve their wildest dreams. But those dreams can be best achieved through a series of progressive, successful steps. With a more conservative approach, rewards are much higher and disappointments are few.

Growers who have experience growing plants in the garden or in pots in the south-facing window are in a better position to start with a more demanding type of plant in your greenhouse. Even if you are experienced, moderation the first time around will yield the best results.

Beginning greenhouse growers should consider vegetative plants like lettuce, basil or coleus, which are easy to grow. Bushes and trees should be avoided by beginners. They each take up a lot of space and take a long time to grow. Quicker production and satisfaction can be obtained from faster growing plants.

Tomato, seedless cucumber, eggplant and hot pepper plants are good for the grower with more experience. Bell peppers, which are a little more difficult to manage to good growth, should be left until some experience has been gained with the other fruiting plants such as tomatoes, cucumbers, eggplant and hot peppers.

Production Systems

There are many potential production systems that could be used in the hobby greenhouse. It is not possible to review each one of them individually in this brief article. Once you have decided what plants you want to grow now, and even in the future, you will be in a better position to choose the growing system or systems to obtain for your greenhouse.

Some systems are designed for growing a few plants in a small area. Only small plants should be grown in these systems. Instructions that come with the system may state that you can grow larger plants. Although the larger plants will grow in those systems, they typically will not perform as expected and will produce less than in a system designed for larger plants.

For larger plants like tomatoes and seedless cucumbers, a system that places the plants on or near the floor rather than up on a bench is best. These plants will require a plant support system to keep the stems trained vertically. The plant systems will need to provide adequate plant spacing for the plants to grow and produce adequately.

Limiting yourself to two or three systems will be best for most small hobby greenhouses. The different systems will accommodate different sized plants, allowing for a variety in the greenhouse. By starting with a few growing systems, the hobby grower will not be spread too thin by having to check over a dozen small systems. After all, the entire objective is to grow well and enjoy the experience!

Fertilizer

A commercially available general hobby fertilizer will do the job for the beginning grower. Although a commercial greenhouse grower will often use customized recipes based on the plant grown and the water being used, satisfactory results can usually be obtained on the hobby level with commercially available hobby fertilizers.

Hydroponic growers will need a fertilizer designed for hydroponic production. The makers of many fertilizers for soil or other media assume that the media will be contributing some of the fertilizer ingredients required for plant growth. In hydroponic systems, however, all nutrients needed for growth must be supplied in the fertilizer. Commercially available hobby fertilizers will usually have a full array of needed nutrients. Flowering plants have increased requirements of certain nutrients compared to vegetative plants. Some fertilizers have different components in separate containers that are mixed in different ratios for different kinds of plants and for different growth stages.

Growing organically is a little more restrictive but still quite possible to accomplish in the hobby greenhouse, however, it will require a higher level of dedication and time. If the grower is personally using the produce from the greenhouse (i.e. not selling any of it), organic certification is not required. Of course, even if you’re consuming your own produce, you may wish to pursue certification as a personal goal.

Generally, an organic media is going to be a little more complex than the media in the hydroponic system. The media provides some of the nutrition and the basic energy sources and environment for the microbial activity that is an important part of an organic media. Some of the additives used will be for the direct benefit of the microbial activity in the media.

Pest Management

The first and best pest management strategy is to keep pests out of the greenhouse from the beginning. Starting from seed rather than importing started plants or cuttings is one preventative measure that was discussed earlier in this article. Installing insect screening on air intakes will reduce the likelihood of insects and mites getting into the greenhouse.

Outside plants and bushes should be kept away from the greenhouse, since they can harbor unwanted pests. If the grower has an outside garden, the greenhouse work should always be done before going into the garden rather than after. Going into the greenhouse after working in the garden can result in insects or diseases being transported in.

Pets that romp around through the weeds, the garden and the neighbor’s yard should not be allowed into the greenhouse. They can introduce unwanted agents to the greenhouse.

Keep a Step Ahead of Your Plants

In this step-by-step approach to your first hobby greenhouse, one of the most important principles is to keep at least one step ahead of the plants. When plants get ahead of the grower, the grower is no longer in control and a stressful situation (for plant and human alike!) has been allowed to develop. Observing the above suggestions will ensure that the grower remains in control and has a satisfying experience in his first greenhouse.

Growers may consider joining a local garden club where the members have similar interests. A new grower should research the clubs and attend meetings to check them out. Some clubs tend to be highly competitive and made up of long time members who have forgotten what it was like to get started; however, most have many members at varying levels of expertise who can be very helpful and supportive of your efforts.

In closing, being methodical, researching and learning along the way, starting out slowly and gaining knowledge through hands-on experience will make the beginner hobby grower’s path rewarding and fruitful.

We are now into late November and have been enjoying 16 varieties of leafy organic greens. In case this is the first time you have glanced at Maximum Yield, this article is part II from a previous article detailing the organic production of baby greens under poly in South Western B.C. The first installment discussed the construction of the greenhouse, raised beds, organic soilless mix preparation, and the brewing of an aerobic organic tea solution (for fertigation).

Some might ask: “well, how’s it growin?” Firstly, I must say that organic greenhouse production in raised beds is by far one of the easiest and least management intensive methods of production I have practiced.

Moisture management is very simple in this greenhouse. I almost never need to water! The average temperature within the greenhouse is near 15°C, and since we are growing leafy greens, the watering requirements are low to begin with. Condensation is not usually welcome in greenhouses, but is a fact of life. With certain coverings and certain installation techniques it is possible to reduce the amount and of condensation within the structure helping to minimize “drip”. Since the greenhouse is covered with single poly, it is fairly airtight. Just for comparison an average glass house loses it’s internal volume of air about every hour, while in a double poly house it usually takes about five hours. This means that as well as trapping heat in the winter, it also traps moisture which condenses on the surface of the greenhouse covering as it is cooler than the surrounding air. The result is sort of like a terrarium. The moisture rises from the beds, condenses on the covering and drips back down into the beds. This has greatly reduced the watering requirements, but is not necessarily desirable.

Firstly, the film of moisture on the greenhouse covering reduces light transmission. In B.C., winter light levels are painfully low to begin with so this is not especially welcome. If greens were not the crop cultivated the moisture dripping from the covering into the beds could create foliar diseases in crops. Luckily, for our purposes this has not proven to be a major problem, although growth rates are probably a little lower due to reduced transpiration from the leaves in a humid environment. The solution would be to install a dehumidifier or provide a timed hourly air exchange, regardless of temperatures. Installing a dehumidistat in a greenhouse exhaust system is not practical during cooler months. The exhaust fan would run near constant, removing all the heat from the greenhouse.

Good air circulation can greatly reduce the level of condensation. However, blowing air swiftly over as much of your covering as possible is not the best idea either. Heat transfer from inside to outside would be increased effectively reducing heating efficiency.

I am also guessing that a lot of moisture is rising from the ground. By installing a sheet of heavy vinyl or polyethylene as a ground covering before adding gravel to the foundation may help to reduce humidity levels.

Usually the only time I have added any moisture to the beds during cooler months has been to apply the organic fertilizer tea. It is added to the reservoir and then applied to the beds. In fact to reduce the amount of moisture added to the beds, I have applied the fertilizer tea undiluted with no apparent nutrient “burn” or imbalance created. I think it’s pretty fair to say that you could not do this with most synthetic fertilizers.

If you are used to working with synthetic fertilizers, switching to organic production methods requires a change of ideas.

It seems through practical experience and analysis that levels of available nutrients in the soil solution are relatively low, while the potential for nutrient levels is very high. For the scope of this article we will address nitrogen, although each nutrient has it’s own cycle. The soil test indicated that there is only 23.75 ppm of Ammonical Nitrogen, and 17 ppm of Nitrate Nitrogen. By all standards this should create a deficiency of nitrogen in an actively growing crop. However, as the soil system is “alive” it seems to be capable of maintaining it’s own nutrient levels near optimal, provided there is a source of food and good conditions for beneficial microbes. Note for example, microbes thrive in lower nutrient conditions, while plants tend to do a little better with higher nutrient conditions. So a total of near 40 ppm plant available Nitrogen is probably near the bare minimum for plants and near maximum for microbes. However, there is likely a high rate of potential nitrogen. Nitrogen, like other nutrients, can be stored in the soil in forms unavailable to the plant but resistant to loss from factors such as leeching and microbial digestion. As available nitrogen levels are lowered by the crop (and some microbes) microbial life in the soil will go to work on the unavailable stored nitrogen converting it to plant available forms. The microbial populations associated with the conversion of the unavailable forms will then reduce in numbers as the nutrient level becomes higher than optimal for their existence. As plants use up the available forms, the cycle continues.

Nutrient availability is also affected by temperature. During the coldest periods, the temperature on the heating thermostat is lowered for heating fuel economy as it will cycle a little less frequently. The soil temperature will drop slightly to 13°C (55°F). At temperatures this low many nutrients, especially phosphorous become less or unavailable. There has been no apparent sign of deficiencies. However, with the exception of a few varieties, baby greens are not a nutrient intensive crop. Although microbial activity is slowed during cooler conditions, I suspect that many nutrients remain available due to symbiotic relations in the soil between the plants roots and microbes. For example, phosphate (PO4) is the form of phosphorous commonly available to plants, although other forms of phosphorous may be stored in the soil. As temperature decreases the availability of PO4 from the soil solution, organisms that live on and in plant roots can digest the unavailable forms in the soil, and exude plant available phosphorous and feed it directly into the plant roots. So, even when soil conditions are less than optimal, some nutrients may remain available in part to microbial activity. However, mass flow (the movement of phosphate across the root membrane) is the primary method of phosphorous absorption and is the most capable of delivering phosphorous when it is in high demand.

The soilless mix and organic amendments break down into humus and finally into to humic/fulvic acids. There are thousands of studies that demonstrate the benefits of humus and humic acids in soils. Firstly, fulvic acids (a light molecular weight fraction of humic acids) greatly increase the availability of many nutrients such as calcium and iron. Not only is their absorption increased, but the plant expends less energy in nutrient transport. Fulvic acids also allow nutrient absorption through a broader range of growing conditions, including pH fluctuations and mildly saline conditions. Humic acids, having a heavier molecular weight are closely associated with water transport and may also encourage root development and assist microbial life.

In examining the nutrient testing results of our soilless mix, it seems that immediately following the tea application, available nutrient levels were actually lowered while the overall concentration of the soil solution increased. I would guess that this may be a demonstration of the idea that a healthy soil solution is self regulating. As the solution was applied it appears to have leached some of the available nutrients away, and possibly triggered the microbial population to convert excess nutrients into unavailable forms (not tested for) that are stored and converted as required. It is also interesting to note that those elements (Potassium, Calcium, Magnesium, Iron, etc) more closely associated with colloids and soil CEC ( cation exchange capacity) seem to be present in relatively higher quantities than those elements more closely associated with microbial activity. However, this may be in part the result of greater nutrient solubility in one component of the organic tea brew versus others. Iron and potassium are abundant in most sources of dried kelp intended for agriculture. However, since most kelps come from salt water sources the sodium level in the soilless mix appears to have doubled.

As for heating, the area is sheltered by trees so it helps to reduce the rate of heat loss through the greenhouse covering due to reduced winds. When it gets below-5°C and the wind is blowing hard, a 25 LB propane tank lasts no more than 36 hours with a temperature set point at 12°C. However, during milder overcast conditions a single 25 LB propane tank can last over five days. When the weather is milder the heating set point is maintained at 15°C as it cycles less frequently and is economical in increasing production rates. During cooler weather the heat set point is maintained at 10°C to conserve heating fuel. Incidentally, there is usually more sun available during cooler conditions so day time temperatures are actually warmer, while nights are cooler due to a reduction in fuel consumption. It has also become apparent that red hues exhibited by some varieties of greens are enhanced with cooler temperatures. If all rows were planted at the same time it may be worth the increase in aesthetic appeal to lower temperatures slightly a few days prior to harvest.

To date, we harvest about one row of fresh organic greens every week.
The flavour, texture, and colour are unbeatable. Obviously, it doesn’t get much fresher than this. The best part is having piece of mind about where it came from and what it was grown with, which in this case is sunshine and TLC.

Fruit size in tomatoes is normally controlled by choice of variety and by a process called truss thinning, in which the number of fruits allowed to develop on a fruit truss is controlled by the removal of any flowers in excess of the pre-determined fruit number. This normally means that mean fruit size is controlled by reducing fruit numbers per truss in the winter, and increasing them in the summer.

However, mean fruit size is not the factor which influences market return, as it the the actual size of the individual fruit which is critical (ie fruit size distribution). Increasing the fruit number per truss during the summer (when growing conditions are optimum) may keep the mean fruit size constant, but there will be an increased range in fruit weights due to the additional number of fruit per truss.

Our study was to examine the relationship between fruit thinning and fruit size (weight) of the individual fruits down the truss in order to develop a strategy to increase the market yield of greenhouse tomatoes. 

The experiment was conducted at the Plant Growth Unit (PGU), Massey University, Palmerston North during March through to December 2001. A greenhouse of 12m X 8 ½m and growing height of 3m was selected. A NFT (nutrient film technique) system was constructed with seven-meter long channels made from pandafilm running parallel across the width of the greenhouse in double rows spaced at 40cm on a slope of 1 in 35. These double rows were spaced at 1m intervals.

Seeds of the tomato cultivars: Alboran (Standard), Ophir (Beefsteak) and Cherita (Cherry) were all sown on March 1, 2001, into a peat based seedling medium. The seed was germinated on a heated (22°C) capillary bench in a greenhouse. On March 13, 2001, the seedlings were pricked out and transplanted singularly into one hydroponic cell. These transplants were placed on a wire mesh bench so the roots would not grow out of the trays.  The greenhouse was maintained to heat at 14°C and vent at 20°C. The transplants were liquid fed every two to three days until planting to ensure continued growth and development. 

The seedlings were transplanted out into the NFT channels on April 11, 2001.  Each cultivar was grown at a density of 27 plants per double row (2.76 plants/m 2 ). On fruit formation Alboran was thinned to three, four or five fruit per truss, Ophir thinned to one, two or three fruit per truss, and Cherita thinned to four, eight or 12 fruit per truss. The truss thinning was achieved by thinning from the distal end of the truss to the required truss numbers. Bumblebee hives were put into the greenhouse every two months to promote good fruit set on all tomatoes. An EC of 3.0-4.0 mScm -1 and a pH between six to seven was maintained daily by the addition of water or a nutrient, acid, or base solution.  Greenhouse temperatures were maintained to ventilate at 22°C and heat at 15°C throughout the whole growing season.

Neem oil with an Azadirachtin content of over 1500 ppm was sprayed once or twice a week to control whitefly infestations. Removal of the bottom leaves up to the last fruiting truss was performed to eliminate any onset of disease. Fresh red fruit weight was recorded at each fruit position in the truss.

We are unclear whether our results are consistent for all cultivars but it is clear from our preliminary results that :

1) the larger fruited (beefsteak) types show a much greater reduction in fruit weight (size) as one moves down the truss, than the small fruited (cherry) types, while the  standard varieties are intermediate.

2) In general the size of the first fruit on the truss determines the size of the other fruits down the truss.

Alboran and Ophir produced slopes of around –13 and -17 (g / fruit position) respectively in all three fruit thinning treatments (Fig. 1 & 2). These slopes produced significant differences between the proximal (first fruit) and the distal fruit (last fruit) in all three fruit thinning treatments. Bohner and Bangerth (1988) and Bangerth and Ho (1984) found that this difference in fruit weight between proximal and distal fruit was because of the natural flowering sequence and the higher number of cells in proximal ovaries at anthesis, with cell number on average 18% less in distal fruit (Bangerth and Ho, 1984). Simultaneously, the higher IAA content in proximal fruit may explain their greater sink activity (Bangerth and Ho, 1984 and Bangerth, 1989). 

Thinning to less fruit per truss resulted in significantly heavier proximal fruit (Table 1 & 2). This difference in proximal fruit weight was then observed down the truss as shown in Figures 1 and 2. This indicates that by reducing the number of fruit on a truss or sink size, the remaining fruit (with more photosynthetic now available to them) increased in proportion to each other within the truss, thus keeping the same slope.

Table 1. Weight of first fruit on truss for Alboran fruit thinning treatments.  Figures within columns followed by different letters  shows a significant difference at P d” 0.05 using LSD test.

  Table 2.  Weight of first fruit on truss for Ophir fruit thinning treatments. Figures within columns followed by different letters  shows a significant difference at P d” 0.05 using LSD test.

 Each truss on the plant was measured for all three Cherita fruit thinning treatments. (Figs. 3 to 5).  It was shown that all trusses up the plant followed the same slope in each of the three fruit thinning treatments. There was also a trend of the earlier trusses having a heavier proximal fruit, and thus heavier fruit down the truss, compared with the later trusses. This was probably the case of the later trusses developing under a high plant fruit load with increased competition for available assimilate, while the earlier trusses had less competition for available assimilate.

Fruit thinning to eight fruit per truss in Cherita resulted in significantly smaller fruit than thinning to 12 fruit per truss as was shown with the proximal fruit (Table 3). No reason can be given for this except that in both blocks of plants, the eight fruit per truss treatment plants were by chance randomly positioned on the eastern part of the glasshouse where solar radiation is lowest.  Therefore the reduced solar radiation would cause fewer assimilates to be produced causing lighter proximal fruit.

Table 3.  Weight of first fruit on truss for Cherita fruit thinning treatments. Figures within columns followed by different letters shows a significant difference at P d” 0.05 using LSD test.

Let us look at an example.

Fruit weights of standard tomato varieties get smaller by about 15 g per fruit as one moves down the truss. If we require a 75 g  tomato, and we have a fruit size of  100 g for fruit No. 1,  then the fruits down the truss are:

Key:      A—5 fruit/truss spring

              B—5 fruit/truss summer

              C—5 fruit/truss winter

              D—7 fruit/truss summer

              E—3 fruit/truss winter

Assume that the premium grade of tomatoes ranges from 55-90 g, then although we get an increased total yield  under good growing conditions by increasing fruit number/truss (D) we do not increase the yield of premium size. 

The answer lies not in increasing the number of fruit per truss, but to increase the number of trusses/m 2 . This can only be achieved by increasing the number of stems per plant (or /m 2 ).

Similar results occur when a similar study was undertaken with beefsteak and with cherry tomatoes.

The difference being that reduction in weight per fruit as one moves down the truss is larger for the large fruited beefsteak type and smaller for the small fruited cherry tomatoes.

It is interesting to note that the yield per truss, and therefore per plant for cherry tomatoes is lower than for standard types, which are in their turn lower than for the beefsteak types.

For this reason it is possible that attempting to standardize fruit size by using “truss tomatoes” types (with their more even fruiting down the truss) may result in lower yields. 

Clearly to control fruit size through the year requires a combination of thinning trusses, but more importantly the manipulation of truss numbers per m 2 .

If there is a premium price paid in the markets for specifically sized tomatoes, then it is clearly economically relevant to develop production systems which will maximize productivity of the premium sizes.

Our work suggests that this is most likely to be achieved by manipulating stem numbers (truss numbers), rather than by manipulating fruit numbers per truss.

Although we did not examine the effect of stem density in our study, it is likely that to maximize productivity, the amount of foliage (leaf area) should be seasonally adjusted, possibly by doubling stem numbers in the summer, compared with winter, with spring and autumn stem numbers being intermediate.

Under these circumstances a constant number of fruit per truss may prove to be the ideal solution?