This 1970's Everlite greenhouse was one of the reasons I bought this house in 1998. One of the past owners grew orchids in here year round and heated the single pane structure; I can't afford that! I can barely afford to heat the old house, built in 1939.
Believe it or not, I cleaned this place up a couple weeks ago to make room for as many tender plants as possible. Most will last at least another month, some will survive all winter and others are brought inside to live on the windowsill for the winter.
It's wonderful to have some summer flowers hanging around for a while, but my favorite plants in the greenhouse are the herbs, specifically basil. I bought a couple flats at the end of the season and now I have the luxury of fresh basil for a few more weeks.
I talk to more and more people who are building greenhouses. They certainly don't have to be as elaborate as mine. Charley's Greenhouses has lots of options and many of them are affordable. A cold frame is another option.
It can be made out of a frame of cheap lumber and recycled windows. Leafy greens can survive all winter in a cold frame, especially if it's located near the house.
Another trick is to dig down a foot under the cold frame and fill the area with fresh manure. As it decomposes, the manure produces heat. Early settlers used those "hotbeds" to keep crops growing through tough winters.
Here are lots of ideas for building a cold frame.
It's fun to have something growing when it's not supposed to grow. Here are some photos of what's going on in the greenhouse.