It’s not yet officially winter, but the vegetative world is napping. Do you miss the aphids? Do you miss them enough to get a greenhouse for them?
Prices have come down significantly in recent years, some of the most modestly-priced from Harbor Freight. A 6-by-8-foot greenhouse is on sale at times for $299 through this vendor. Check for shipping charges on any greenhouse you want to buy, because those charges can be substantial.
You can also build your own of polycarbonate panels or recycled materials, but there are a number of other things to consider too.
Would you want a stand-alone greenhouse or an attached lean-to? The stand-alone has more growing space than a lean-to, but the lean-to is easier to access, wire and plumb. Yes, you will need a water source unless you want to carry water. Remember, water is heavy. My greenhouse is a lean-to, attached to the house. When we added onto the house, we moved the furnace from the crawl space to the new basement. That required some duct changes, so I had the furnace fellows route a duct to a foundation vent at the greenhouse site, providing some warmth in the greenhouse.
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Consider our winter sun. It’s low in the south during winter, so if you’re counting on winter sunlight to grow or continue to nourish plants, they’ll have to be within the sun’s rays. That means a southern exposure. The ancient cliff dwellers of the American Southwest found their southern exposure and stone held the heat, keeping them reasonably warm and comfortable during winters. One of the best ideas, I think, is a partly subterranean greenhouse, at least about 2 feet below the surface of your soil. That will partly keep the greenhouse warmer than outdoor air, but winter sun may not reach the floor.
Those of us in this part of the country think first of heating a greenhouse, but we should also consider cooling it. Our winter sun is bright and hot, the temperature in my greenhouse shooting above 100 degrees F., even when there’s a foot of snow on the ground. Unless the structure can be cooled, plants may be cooked. I don’t know what people with “sunrooms” do about cooling. The notion of cooling seems to mystify some people who sell sunrooms.
My greenhouse is a commercial acrylic structure, a SunGlo, that came with an exhaust fan, a louvered “window,” an electrical panel, and a bench supports for the long wall. We filled in the bench with plastic-coated wire closet panels. The interior is a wavy acrylic wall, similar to the corrugations of cardboard, those corrugations providing air as insulation. I have an electric heater on thermostat in the greenhouse, but can’t really estimate the heating cost since cooling also adds to the electric bill.
We erected the structure ourselves, but hired an electrical contractor to wire it. Plumbing had been installed there when deck construction concealed another faucet.
A greenhouse should be longer than it is wide, to give more east-west sun exposure time to heat the structure. Some say a greenhouse ideally should be three times longer than its width. Ours is not, being 17 feet long by 9 feet wide. Size was dictated by space between desirable tree and deck. Ours has a concrete floor with a French drain. Were I to start over, I would not have a concrete floor, preferring to plant some things such as orange trees or even tomatoes in soil.
Pay heed to the pitch of the roof and the height of the walls if you’re repurposing building materials. It’s been years since we had truly heavy snows here, but in case we have an unusual return of deep snow, your greenhouse roof must be able to let snow slide off, and not pile deep along the south wall, especially.
Once you build a greenhouse, it’s a very pleasant resort during sunny days, amid the gift of greenery, although you will come nose to nose again with aphids and white flies that entered through louvers, even occasional sneaky slugs that flatten themselves to slide under the foundation “plate.” But this is the time to think about it.
Send garden questions to firstname.lastname@example.org or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.