In our eagerness to get back to gardening, many think seriously about getting a greenhouse. A greenhouse may not be as costly as you fear, and I think a positive in property value.

Think outside the house, to start with. Here are some innovative solutions to building a greenhouse yourself out of recycled windows, for instance:

Dig a trench the size of the greenhouse you want, and just use old windows or polycarbonate panels from about knee high on up. Use your computer to search for polycarbonate panels for price and structural comparison, watching out for shipping costs. If they're to come from the East Coast, you know shipping will be high.

Part of the structure below soil level gives you the insulating factor of surrounding soil. You should build walls inside the trench though, probably masonry, so a gopher doesn't burst through. I don't think they'll set runs 3 feet deep, below a masonry wall.

Or build a garden shed, one-half greenhouse, the other half tool storage. You may be able to buy greenhouse-grade fiberglass panels locally for roofing.

A hoophouse covered with heavy clear plastic is an inexpensive option. Great instructions are here: www.westsidegardener.com/howto/hoophouse.html .

A covered hoophouse without supplemental heating will shield plants from a few degrees of frost (providing plant leaves don't touch plastic, for it does conduct cold).

You could use Visqueen plastic sheeting, then if you like your new growing space, buy more permanent cover. If you don't want a squared top, you could buy benders for chain link fence top rail. Johnny's Selected Seeds sells the bender for about $60, and the rail is available locally. A group of gardening friends or a club could buy the bender with pooled money, sharing the benefits.

A clever fellow could build a bender for conduit for a hoophouse, too.

Be sure to situate any supplemental growing structure on the south side of your house.

HEATING AND COOLING A GREENHOUSE

Heating any greenhouse is actually most economically done by just heating the bench you set plants on. If you can figure a way to set up a radiant heating grid, it will be the most economical way to do greenhouse gardening.

Many greenhouse owners, including me, use electric heat with a fan in the greenhouse. How costly is it? I can't tell, because cooling also is a factor in electricity use. On any bright sunny day, regardless of outdoor temperature or snow level, the temperature in my greenhouse easily exceeds 100 degrees, triggering the cooling system. That consists of ground-level louvers and an electric exhaust fan at the other end of the greenhouse working together electrically.

Cooling should be a major consideration. Some companies build "sun rooms" that I presume could get to 100 degrees and hotter on a sunny day, with no provision for cooling. If you can't cool the space, you may cook your plants.

THE KIT OPTION

If you can spend a little more, consider greenhouse kits. Glass greenhouses are the most attractive, but they're costly and much more vulnerable to breaking than structures covered with acrylic or polycarbonate. Again, watch out for shipping costs, because these kits are heavy.

My greenhouse is a SunGlo, originally a kit. It's a lean-to, attached to the house. When we added on to our house, we moved the furnace to the new basement, and some ducts were re-arranged. I had them direct one to a former foundation vent, so that duct funnels warm air into the greenhouse, supplementing electric heat.

I love the SunGlo greenhouses because the interior wall is a deep corrugation, air spaces of at least 1 inch in depth that serve to insulate. The exterior is very heavy acrylic, shrugging off hail, rocks, baseballs and golf balls. The kit included the exhaust fan, louvers, electric breaker box and bench running the length of the greenhouse. The bench is plastic-covered wire, similar to that in closets, easy to clean.

WATER AND LIGHT

Another major greenhouse consideration is water. If you can have an in-greenhouse source, that's ideal. I know some folks fill garbage cans with water before shutting off hoses, but they should be capped to prevent intrusion by hair snakes, mosquitoes, etc., and dipping water can be wearisome.

You won't be able to grow tomatoes over winter in a greenhouse unless you have supplemental lighting, because of the angle of the sun and the lack of sunlight for more than 10 hours for about three months.

Lighting may be as simple as a fluorescent fixture on a timer (12 hours should be OK), with one bathroom light and one kitchen light, set within four inches of your plants.

You should have the capability of raising the fixture as the plant grows, such as by hanging it from S hooks on a chain.

Send garden questions to melauter@earthlink.net or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.