Slowly but surely, spring is drawing nearer. Denver weather being what it is, we have been on a roller coaster ride between warm, sunny days and cold, snowy ones. But by mid February, it will be time to plant our high tunnel / hoop house greenhouse on the Littleton Farm. It is a simple, Eliot Coleman style structure, with PVC pipes covering rebar rods for the frame, and a layer of plastic stretched over it and buried on each side.
Denver is a different climate then Maine, where Eliot Coleman pioneered this type of structure. There is a greater chance of hot weather in mid winter and a stronger sun. (Last February, as we built this greenhouse, it was 80° F and sunny. ) These warm spells can give way to intense cold and high winds with little warning. Even the average winter day can have a fairly dramatic temperature swing over the course of the day. So we will be adding some thermal mass to the hoop house to damp down these swings, in the form of some 55 gallon barrels full of water, and some insulation to the North side. We also have to repair some storm damage, and we will be replacing the flap style entrance with a real door that will help seal out the weather.
Last year we grew in the soil of the hoop house. This caused several problems. The soil is not that great. It is infested with very persistent weeds, including bindweed and prickly Buffalo Burr, which were hard to sort out of the salad crops. Because of the low headroom, the central path had to be lower then the beds on either side. This tended to drain water off the beds. Finally and most seriously, the hoop house quickly became too warm for cool season crops in the spring, long before they were finished. Warm weather crops could have been planted, but the cool season ones were in the way. The same thing happened in reverse in the Fall; by the time the warm weather crops froze out, it was too late to start cool season ones.
We thought about remodeling the hoop house so that it would be movable to counteract this problem. However, that solution would be expensive and take quite a bit of work. We might do it once our current tunnel wears out, in another few years.
Instead, we are going to experiment with containerized growing in the tunnel, using food grade 5 gallon buckets that can be obtained free from bakeries. Our concern is that they will increase the soil temperature swings, and we will try to avoid this by burying them in either sand or woodchips. But otherwise they should solve all our problems; we will incorporate water reservoirs and use prepared potting mix. And when the weather outside warms up, we will move the buckets of salad out under row cover and move in new buckets to get a head start on growing eggplants, peppers, and sweet potatoes. Similarly, cool season plants can be started outside in the Fall, ready to move in as soon as the warm weather crops freeze out.
We will let you know how it goes!