Last Christmas I received a book by Eliot Coleman called Four-Season Harvest that talks about how they grow vegetables all year around using plastic greenhouses (hoophouses) and a single layer of floating row cover in the coldest months. Eliot and his wife, Barbara Damrosch, live in Maine in zone 5 which is the same zone as in Cedar Rapids, so I was compelled to do my own four-seasons experiment in my backyard this winter. I started with a small greenhouse (6x8) that I bought at Menard's in March that was on sale from the previous season. It was $89 with a simple metal tubing/plastic construction that didn't take my husband long to put up at all. We erected the greenhouse over the existing garden in a location that receives the most sunlight during the winter in late September after the pole beans and tomatoes were removed. We planted some mesclun mix lettuce, spinach and mache to see how they would do.
We harvested the lettuces early in the season and they supplied us until about November. In early December, we thinned out the spinach which was baby spinach size. Unfortunately, the growth in the spinach stopped and now we are left with spinach too small to harvest. But it is still green and unfrozen! A tremendous thing since the temperatures have already dropped below zero degrees on many occasions. The mache or corn salad seems to enjoy the cool temperatures and I swear is still growing. So far, so good. Hopefully, the small spinach will begin to grow again in early spring and we'll have spinach salad in March. Note to self for next year: Plant earlier so plants are bigger before the temperatures dip into the 20s.