The evolution of greenhouse growing is at an all time high. The concept of running a greenhouse in the summer and the winter have taken on a whole new approach. What’s the difference?
Winter – Most people realize the advantages of a greenhouse when it’s cold. A greenhouse in the winter can play a crucial role in providing gardeners with continued use or season extension. During the day, the sun warms the air, plants and soil. At nighttime heat is needed. In order for this process to be efficient or even work for that matter, the greenhouse must be sealed, with only ventilation fans and intakes as the source for fresh air. With supplemental lighting and some heat, a more ‘controlled’ environment is achievable. What is meant by ‘controlled’ is trying to control the environment to keep the crop happy. The air temperature feeling right doesn’t mean the soil or water temperature is actually ideal for the plants. Adding lights and above air heat, we have experienced up to 40% DECREASE in production.
Summer – Who would have thought that would even be a statement? FFG has clued into some helpful ways to work with the summer heat. One big difference from the sealed winter version is now a more open and naturally ventilated greenhouse. Some simple ways of naturally ventilating might be taking the end wall coverings down or re attaching the sidewall covers a few feet off the ground to improve more airflow. Lets face it, we all know what its like to be in a car with the windows rolled up on a hot summer day. This is the reason for our diffused greenhouse coverings. The polyweave greenhouse covers and the rigid twin wall or corrugated polycarbonates are all 100% light diffused.
Diffused light has a positive influence on production, especially during the summer. This positive effect can be explained by a change in light penetration into the crop and by an increased photosynthesis capacity. A crop like cucumber can utilize diffused light better than direct light. In addition, diffused roof material results in a lower crop temperature, especially higher in the crop which likely leads to more optimal conditions for photosynthesis. The polyethylene/polyweave covers are stronger and last longer than normal film. Greenhouse film is usually 4-6 mil plastic that is very easy to puncture. We see it in landfills more often than the polyweave material. The film is quite a bit cheaper but the longevity and the problems people face using them in the summer are not worth the savings.
The majority of people think glass is the ultimate greenhouse covering. I would say if you are in the Netherlands or somewhere especially cold year round, glass is great. Glass does not insulate, therefore it can be an expensive way to cover your greenhouse and making it LESS efficient at the same time. It’s twice the cost of polyweaves and poly carbs. Glass in the higher elevations tends to magnify the light, which in turn creates hot spots on the leaf surface of the plants.
As the greenhouse warms up, the plant begins to transpire by bringing the water from the roots to the leaves, a natural way a plant cools or protects itself. Once the water transfers to the leaves, we begin to see humidity increase or the plants begin to sweat. At first this process can be protective to the plant and as this process continues we see more problems develop. The humidity creates water droplets or condensation on the inside of the greenhouse roof. Rain on the inside!! Those droplets also act as magnifying glasses all over the roof which create hot spots & the potential for mold. I’ve even heard of power outages in the middle of the day rendering exhaust fans and circulation fans useless, which is a recipe for disaster. A simple diffused polyweave or diffused poly carb would have helped this situation and is half the cost of the glass. The twin wall polycarb is a better insulator than glass so it is much more efficient. Another reason people like glass is the idea you get more lumens. In some ways that is true, however the sun is so intense that in the heat of the summer you will actually gain more light by diffusing it rather than going in direct sunlight. By diffusing the light we are taking a light particle and breaking it into more light particles that can actually penetrate deeper into the canopy and provide more light to the lower branches.
The ideal greenhouse for summer can be anything with a diffused cover and is well ventilated. Favorably, something with roll up side walls and doors at both ends. That way you can avoid the solar gain, cool the plants and the soil (even if the air temps are in the 100+ degrees) and keep the air fresh. Stagnant air that is heating up is what you are trying to avoid. Having a house with a roof vent is also a very good option. Roof vents allow you to release hot air that can gather in the peak. This will keep the cooler air lower in the greenhouse. On a hot summer day, ideally a greenhouse with a ridge/roof vent, roll up sidewalls and doors on both ends allows a person to open up and avoid the solar gain and in turn cool the plants and the soil. That will result in decreased plant stress and continue photosynthesis when outdoor plants suffer, and you don’t even need to run the big exhaust fans or evaporative cooling systems. Some small H.A.F. fans might be all you need throughout the heat of the day.
Evaporative greenhouse cooling systems are like a swamp coolers. Water runs over a thick pad on one end of the greenhouse while exhaust fans pull air from the other end through the wall of water. They work well in moderate temps and dry areas. Since the fans run off of water, humidity can rise which isn’t always wanted. The electric bill for cooling a greenhouse is also another issue. These systems are useful in dry, hot climates. So far we have found that the majority of greenhouse companies outfit greenhouses for cold/winter use only. It never occurs to them you might use it in the summer. In some areas it might be best to swap covers from winter to summer. The polyweave in the summer will protect you from rain and sun’s intensity. However if you are in a colder climate, switching the cover out to a double inflated poly film could add to the efficiency of the wintertime use.
Circulation fans are another very important part of a greenhouse. Some people find themselves near the coast or a foggy mountain area that gets higher humidity in the morning or evening. Horizontal airflow fans or H.A.F. fans are the key to drying out the air. Take Florida for instance. They have pretty good humidity even on a warm day. You can’t fire off a heater to dry out the air. The H.A.F. fans actually get the air moving in a direction rather than oscillating fans scattering the air movement. The air will dry out faster and more efficient if moved in a direction. Most other greenhouse companies recommend fewer fans but we see the benefit of adding more circulation in this department, for dryer, fresher air. Adding Light deprivation or blackout to a greenhouse is another important factor to increasing productivity. Normally growing outdoors or in a greenhouse, we have to wait until fall for the harvest season. With a light dep. or blackout cover, you can force flowering as early as July!! The light dep. cover can be manually pulled over the garden or greenhouse. As long as you create the correct light cycle everyday you should be able to harvest way before mother nature intended. Internal and external systems are optional.
For internal systems we recommend a breathable blackout material. This in turn helps avoid any condensation drips that can occur after the curtain is pulled. Remember, the fans and intakes will be restricted because of the light leaks. With that being said, it’s obvious we are going to see a bit of a heat and humidity spike since the sun is still out and were covering our crop. For external systems, we recommend a non-breathable blackout material. If you have a greenhouse cover and you try to pull the breathable over the outside, it won’t breathe. The same issues with ventilation will occur. The next step was to use underground ventilation since we cannot go through the walls of the blackout; we are cut off from those awesome exhaust fans we might use throughout the day. Going underground also means a bit more work upon installation. If you already have a greenhouse, this might be a real pain to install.
A new solution has just been created …………. FFG has unveiled a new product called The Breathable Wall. The Breathable Wall was created to allow full air flow through your exhaust and intake WITHOUT light getting through. We basically created a baffle that breaks up the light and not the air. Even indoor growers find the benefit of The Breathable Wall for covering holes in walls for vent and a/c systems. We see customers building end walls on their greenhouses so they can pull a black out cover over the roof and sides while leaving the ends to breathe (Day or night). The Breathable Wall can also be placed over the exhaust and intakes. The end walls would be covered in something solid like plywood. Instead, using The Breathable Wall, you can pull the cover over the roof and sides and still create the same air exchange as the daytime. This has never been achieved in the light dep. world till now.
When shopping for a greenhouse you have many options. Price should not be the only factor in purchasing a greenhouse. Always look for reviews, check to see the thickness of the frame. The type of framing, rolled steel, tubular or square. Make sure the greenhouse can handle the wind/snow for your area with all of your desires met. Greenhouses can start out really basic and can be upgraded over time. If you can’t afford the roll up walls now, add them next season. You might need to keep your screw gun handy because you can always re attach the cover to the ground when its gets chilly. It may cause a bit more work but in the long run it can save a few bucks.
The problem with buying your greenhouse from a Big Box dealer is that the catalogs may show a nice picture of an ideal greenhouse but as you start to place your order, you’re not actually getting what’s in the picture. We run into this all the time, our customers have purchased from somewhere else and didn’t get what was expected. You might get the frame and cover but not the doors or the roll up walls. Or if you get the roll up walls you have to get the polycarb roof separately.
The greenhouse should not be the “cheapest” thing on your list. Keep in mind that most greenhouse companies can sell parts for you to do it yourself. The covers, locking hardware and other miscellaneous parts might be all you need to create a growing area that suits your needs. The greenhouse is your #1 offense and defense against weather, security, privacy and sustainability. Get quality parts and info from people who care about your passion for gardening.
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