There are a couple of tomato plants in my greenhouse this year. It's covered with UV resistant plastic film. The fruit is so nice! The plants have suffered a bit from the heat thru the growing season altho' I had it completely open. Everything is closed up now, I'm not turning on the heat but the plants are still doing fine.
I've used Reemay row covers in the open garden. The problem there was the wind and keeping that fabric in place. Still, now that I've seen the difference between tomato plants with full exposure in the open ground and how those in the greenhouse have done - I am wishing that I could grow tomatoes and other things with a little more protection.
Reemay comes in various thicknesses. The heaviest at 1.5 ounces/yard is supposed to protect plants down to 26F as a row cover. It might work better than that on a frame higher above the plants. You could use a heavy tarp or some type of thermal blanket to cover a small greenhouse overnight.
These ideas don't seem adequate for my northern location. I would have problems both with heat and light penetration with the Reemay. It is supposed to cut out 50% of the light with the heavier fabric. That compares to about 10% loss with plastic film and it could be a real problem when there are few hours of daylight or where spring skies are cloudy.
If you are only dealing with winter temperatures down into the 20's or just plan on using a greenhouse for a few weeks before the last spring frost - a row cover fabric might be a way to go.
Steve
