ChiloquinNews article 4/18/2011
At first thought this seems like an impossible task, but it may not be quite so impossible as you think.
The first requirement is a sunny location to grow outdoor vegetables in the summer. The second requirement is a south-facing, sunny location for a greenhouse. What you can grow in your greenhouse will depend largely on how you have set it up. Thirdly, you need a way to store a lot of that summer produce for use over the winter.
To make maximum use of the sun, the long side of your greenhouse must face south, but there are still other considerations. Will you heat it in the winter? If the greenhouse is freestanding then the cost of heating will be exorbitant, unless you have a big enough structure that you have the space to incorporate passive solar features, like water columns to store heat, and an insulated north wall. If the greenhouse is a lean-to, attached to the south wall of your house, then heating is much easier. That is how my greenhouse is set up. I have a reversible fan through the wall of the house and a thermostat in the greenhouse. When the greenhouse temperature drops below 400 the fan turns on and blows house air into the greenhouse. I also have a 55 gal drum of water to help moderate the temperature. I would have liked to have had several, but then I would have had no growing space. The lowest temperature I have recorded in the greenhouse is 260, when it was below zero outside, and my home heating cost is quite low. If the sun shines at all, even on a frigid day, the greenhouse warms up, and I reverse the fan and send that warm air into the house.
Other things that I have done are to bury 2” thick foam insulation 2’ deep around the outside perimeter, and bury a heat cable around the inside perimeter of the greenhouse. The cable is plugged in to an outlet that turns on at 320; a little added insurance to help keep those plant roots near the outside edges from freezing.
If you have a freestanding greenhouse with no additional heat source, then you may extend your growing season, but I’m not sure that you would be able to actively grow anything from about November-March. If anyone is doing so, please let me know because I’d love to hear about it. If you have a solar greenhouse with enough heat storage to keep the lows above freezing for most of the winter, then you can be growing cool season vegetables for much of the winter.
You must also consider how you will deal with the heat in summer, because many vegetables, even heat-loving varieties, will not grow if they get too hot. Putting shade cloth over the greenhouse is not a good idea if you want vegetables. They need sun, not shade. So the only option is ventilation, ventilation and more ventilation. In my 18ft long greenhouse I have 3 automatic ground level vents and 3 automatic roof vents, which open when the temperature reaches 700. Two thermostated window fans, set to exhaust air, hang under the upper vents. One turns on at 750 and the other at 800. There is a third fan that runs constantly so that there is always some air circulation. When I first set up the greenhouse, with vents but no fans, the temperature went to 1100 on the first mildly sunny day. Now it rarely goes above 900, and is usually somewhere in the 80’s.
Then there is the issue of ‘bugs’. Whiteflies and aphids will love your greenhouse every bit as much as you do. Luckily, there is a little store in Medford, named ‘Nature’s Control’ and painted to look like a ladybug. Their ‘good bugs’ certainly live up to their reputation. Then I should probably mention the Oxalis that got away from me last year, and that I’m still fighting because I let it go to seed… At least I can stay warm as I fight!
There’s so much to say on this subject that I have to divide this into two parts. Next issue I’ll talk about when and what you can grow in the greenhouse.