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Backyard Greenhouse Basics

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The daydream of having a climate-controlled growing space of your own is a pleasant fantasy

Living With a Backyard Greenhouse

Have you ever considered having a home greenhouse? It’s certainly an appealing thought. Perhaps you could start your vegetable garden and bedding plants extra early from seed, saving money and getting the jump on the gardening season. In your wildest dreams you could over-winter delicate plants, or get extra years of life from your ferns, geraniums and poinsettias, or even harvest fresh vegetables in the dead of winter. From the smallest, cheapest greenhouse kits to elaborate “sunrooms” attached to your house, the daydream of having a climate-controlled growing space of your own is a pleasant fantasy.

Let me share some of our own experiences. For many years we had a retail garden center, which eventually had four greenhouse structures. We bought plants from a variety of commercial growers, who had production greenhouses and over-wintering “hoop houses” of all kinds. From all these experiences we learned a few basic rules, and we saw many interesting solutions to common greenhouse “issues”.

First, the number-one challenge of greenhouses is NOT keeping them warm. It’s COOLING them. Sunlight can make a greenhouse uncomfortably hot in minutes; most kit greenhouses are better described as solar furnaces. Ideally your greenhouse should be located where a shade tree will protect it from the hot afternoon sun. Hot air rises, so the ideal greenhouse is “gable vented”, meaning that the peak of the roof can open wide. The sides of the greenhouse should open wide to allow cool air in at the bottom, creating a “chimney effect” that draws air up and out. The greenhouse should be covered with shade fabric, particularly in summer. Fans are needed to keep the air moving.

To keep your greenhouse warm on freezing cold nights takes a lot of energy. The ideal heater is a “salamander”, sitting on the floor (hot air rises), running on propane or kerosene, with a powerful fan to circulate the air. You’ll quickly find that, unless it has “double wall” covering, condensation inside the greenhouse is a huge problem. The cheapest greenhouse covering is clear “poly” film, but you must use two layers. This requires a “squirrel cage fan” to maintain air pressure between the layers of poly covering; the air space acts as insulation.

Your greenhouse should have some sort of flooring. Compacted gravel with a tough “geotextile” fabric is the cheapest solution. Pavers set in clean gravel will last longer. The important thing is allowing water to quickly seep through the flooring material and drain away. A dark-colored floor will store heat, releasing it at night, equalizing the temperature, but this can work against you in summer.

Ready-made greenhouses are a real temptation; local shed builders can deliver one and set it for you. Do-it-yourself greenhouse kits are easily available, and some are fairly cheap to buy, but the spending only starts there. Either way, dealing with the real-world problems will take constant effort and cost real money. Unless your greenhouse is well-designed, you’ll quickly become frustrated with the necessary time, money and effort. All too often, homeowner greenhouses are designed to separate you from your money before you understand how great the challenge actually is.

Steve Boehme is a landscape designer/installer specializing in landscape “makeovers”. “Let’s Grow” is published weekly; column archives are online at www.goodseedfarm.com. For more information call GoodSeed Farm Landscapes at (937) 587-7021.

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