Wednesday, February 21, 2007

Greenhouses: Getting Started

Location Though placing a greenhouse directly in sun exposure is optimal for many gardeners, it really depends on what you want to use your greenhouse for. You may want to use your greenhouse for starting seedlings or plant propagation; in this case you’ll want to place your greenhouse in partial shade. If such a space is unavailable to you, you can use shade cloths to promote shading.

If you are going to use the greenhouse for growing into the colder season, you’ll want maximum sun exposure. A spot with full southern exposure is best for this. Of course if you lack space in a southern exposure you can make up for heat with artificial heating/lighting, though this will be a more expensive solution. A rule of thumb for sun exposure is to secure at least 6 hours of full sunlight a day. Remember to keep in mind that the sun rests in different positions throughout the year. It is higher in the summer than the winter. A spot that seemed perfect in June may be a problem come January.

Try to place the door of your greenhouse in a direction away from which the wind blows. If your wind typically blows up from the south, face the door north to limit breeze entrance and heat loss. Also remember that shadows cast by any trees or buildings around your greenhouse will change throughout the year. Long shadows can mean sun blockage for your greenhouse plants! You’ll want your greenhouse to be easily accessible through all seasons. You can save your back a lot of stress from carrying soil, water, etc., by making the path to the greenhouse level and short. Make sure that the site you prepare for your greenhouse is also level to prevent stress on the structure and leakage problems.

Heating & Ventilation What type of heat are you considering for your greenhouse? There are plants that love tropic humid environments, while others thrive in hot, dry conditions. Whichever types of plants you decide to raise you will be able to experiment and control your greenhouse temperature through a heat control unit. Gardeners tend to use electric or gas heaters. With a gas heater it is extremely important to remember to properly ventilate, not only for plants, as it can give off deadly fumes, but for you, as you work. Electric heaters also have their drawbacks. One major drawback is cost. Another drawback is if the power goes out. The loss of heat in a greenhouse could mean certain doom for your plants as they freeze overnight in winter. If you are going to use electric heat, have a back up heat source so as not to loose your entire collection of plants in the hours following an outage. The newest heat systems, combined with polycarbonate panels,’ work together to successfully control the environment within a greenhouse. Automated systems do not rely on concrete or brick to absorb heat for overnight cold spells.

Heating Tips There are a number of ways to cut down on greenhouse energy costs during winter. Wrapping greenhouse walls with bubble wrap cuts down on heating costs. The bubble wrap works as an insulator. Placing large containers of water in the greenhouse or using 4-6 inches of stone or pea gravel as flooring are both methods of absorbing heat during the day that is naturally released at night. If you live in a colder climate, or if you are considering buying a commercial sized greenhouse, consider building the foundation below frost level. A greenhouse overrides the natural cycle of weather. It does so by utilizing the energy of the sun. In the coldest times of winter you will want your greenhouse to remain above 50 degrees. Using the sun's power you should only need to add additional heat on rare occasions. You can grow any type of plant you want in a greenhouse, or in a cold house, without the addition of too much heat if you simply watch the seasons; know when the sun is strongest and which plants thrive in what type of sunlight. If you are planting tomatoes from December through February you will find that you need to add supplemental lighting for your plants to thrive unlike March to May when your crop will thrive on sun alone. From October until February is the cold season, and from March until September is the warm season. Adjust for heat intensity as the weather goes.

Cooling Tips Harnessing the sun’s energy in the summer months creates the perfect environment for tropical plants, squash, melons and long season squash and melons. With proper ventilation you can continue to grow plants, vegetables and fruit through the summer while you also work in your outdoor garden area. Cooling your greenhouse, at times, may seem a little more difficult than heating the greenhouse. Once you have survived the first year and are more familiar with how your greenhouse reacts to your climate, knowing how and when to increase heat vs. ventilation will become second nature. No matter which type of greenhouse you buy, all greenhouses will need some type of ventilation. A minimum of two vents, one on the roof and one on a side will stabilize the environment in the greenhouse. If you find that you need additional venting you should keep in mind that you can cut glass/polycarbonate or plastic panels, you can also drill holes into the framing of your greenhouse but you should NEVER cut the framing of a greenhouse to insert a fan. This will compromise the stability and strength of your greenhouse with devastating effects. If you find that you have no other alternative, consult with your dealer for a more appropriate venting system. Cross ventilation helps prevent the greenhouse from overheating. An exhaust fan or any shutters should be situated so that they can take advantage of prevailing winds. Generally an 8 x 12 greenhouse should have a combination of roof and shutter vents that equal in size to approximately 20% of the total greenhouse square footage ... remember your open door can count as part of that percentage. Cooling of greenhouses can easily be accomplished using evaporative coolers, exhaust fans, misting systems and shade cloths. Evaporative coolers are typically recommended for extremely warm areas. Typically misting systems, shade cloths and exhaust fans are adequate for cooling in moderately warm areas. You do have choices in ventilation for your greenhouse, including electric or solar powered vents. Ventilation systems are controlled so that if you are away from home when the temperature goes down the vents will close automatically. A thermostat within the greenhouse triggers an automated ventilation system. In every type and style of greenhouse it is important to have at least one (two is better) -roof vent. Using roof vents combined with automatic openers will ensure that you don’t forget to open the vents, or if you go away for a period of time your ventilation system will still be activated. A choice productive for cooling is a thermostat-cooling fan which evenly circulates air in a greenhouse. You should have a battery back up in case of power outages. Ventilation is most essential for plant growth in your greenhouse because plants need a continuous supply of carbon dioxide to continue growth. Without carbon dioxide your plants will surely die. As you keep the airflow in the greenhouse fresh and flowing, you also are keeping diseases and insects at bay – as they tend to thrive in a stagnate environment. There are a number of solar-powered vent openers that are filled with a waxy substance that expands when it heats up and contacts when it cools. The ones that I use begin opening at approximately 65 degrees and are fully open by the time that its 80 or so degrees. Automatic vent openers are one of the greatest greenhouse inventions. They are generally solar-powered (designed to open as the greenhouse air heats up) and require nothing more than simple assembly. Just remember to take the wax-filled cylinders inside during the winter when it freezes - the cylinders can explode if frozen so by bringing them inside you can extend their life and get more for what you pay for.

Greenhouse Irrigation No matter how you look at it, your greenhouse needs functional access to water. If you have a direct water hookup to yourgreenhouse you may even consider using a misting system. This is especially beneficial if you live in an area where the temperature is high throughout the year. The best thing to do is to install water lines before the erection of your greenhouse. This will save you from additional problems after the greenhouse has been bolted to the foundation. If possible you should put the water line below frost level to protect pipes from freezing in the winter. Depending on your soil type and choice of flooring you may also need to install water drains around the greenhouse. How far the water source is from your house will determine the pricing for installing water in the greenhouse. Still, the price is worth it: Some of the main "in the greenhouse" water uses include: rooting plants in water containers, watering plants, misting plants, cooling bricks / concrete to create humidity, and cleaning pots, containers and the greenhouse itself. If you are going to use your greenhouse during the cold winter months, you will find accessories available that are frost and freeze proof, though if you find that you are having problems with lines freezing you can drain the system and carry water manually until they can be "thawed’ out and fixed the following season.

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