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You can spend just about any amount you wish in building your greenhouse. Much of its cost depends on its visibility within your gardens. If all you need is a growing structure, you can nail a few frames together and cover them with clear polyethylene plastic. If you’d like a spectacular glass house, by comparison, go Gothic and buy one of the Old-World-style arched conservatories. Or, for more practical budgets, stop off somewhere in between.

Lean-to greenhouses are especially functional. They give you a rigid support for your house, plus they provide a solid wall, hopefully to the north, that will insulate against the cold winter winds. They usually allow you to tie into utilities from the house or garage, an added savings and convenience.

Free-standing greenhouses will require more substantial structures. Use either preservative-treated wood or aluminum as the supports, then cover your greenhouse with a clear material that will admit all the winter sunlight. Glass houses are obviously the most attractive, but you can also use polyethylene plastic (consider the more expensive sunlight-resistant types that will last for as many as three winters) or one of the clear rigid plastic materials. Fiberglass was popular for many years, but folks have found that it discolors and darkens with age, not good for plants you’re trying to grow.

Your first greenhouse is going to be too small. It never fails. About the time you get it filled, all the plants start to grow and you need more room. That’s when your spouse’s best friend calls and asks if you’ll overwinter the big Boston fern hanging basket. All of which is to suggest, think big. Build a larger greenhouse than you initially planned. You’ll never regret it.

Some folks call them “tables,” but since you’re about to become a greenhouse specialist, learn the term “benches.” You’ll want strong ones to hold up all those valuable plants. Pressure-treated pine holds up well, or you can use welded wire secured to treated pine frames. Whatever you use to build them, be sure water drains away from them quickly and that air circulates around the plants freely. Benches should be no more than 42 inches wide if you’re reaching from one side and 48 inches if you’re reaching from both sides. Keep them at waist level for easiest working of your plants.

Aisles between your benches should be wide enough to accommodate you and any load you may be carrying, but no wider than necessary. That’s valuable space that you pay to build, heat and cool. Don’t waste it in wide aisles. You probably won’t need to bring a wheelbarrow into the greenhouse, for example, unless the house is quite large. You won’t need a potting bench, although you may want to rig up some type of a portable potting shelf that can straddle the aisles while you work, then be lifted out of the way the rest of the time.

Use overhead and wall space as efficiently as you can. Hopefully your greenhouse will have substantial supports overhead, so you can hang those big baskets safely. Try not to block all available sunlight from the plants below, however. Along that line, if you’d like to use a side wall for wall pots and baskets, let it be a north wall, so they’ll get full south sunlight without getting in the way of light to the other plants.

Provide an efficient heating and cooling system for your greenhouse. Small houses can be heated with vented space heaters, but you’ll need a fan blower for greenhouses larger than 200 square feet. Evaporative coolers or fan-and-pad cooling systems are best for beating the summer heat.

Provide ample faucets and electric outlets in your greenhouse. You’ll want to be able to water without dragging a hose in from the outdoors. You may want a mist system, nighttime lighting or other electric devices, so be sure your greenhouse is amply wired. Install a temperature alarm thermometer as well, to let you know when the heating or cooling system isn’t working properly.

Posted by Neil Sperry
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