Covering a garden bed with a cold frame or low tunnel is an easy way to extend your growing season by months in both the spring and fall. While most people aren’t going to build a bioshelter in their backyard, this is an easy, quick, relatively cheap, and highly scalable way to get a little more food out of your garden.
In late October we build this low tunnel over one of our beds in less than an hour. There have been many nights below freezing since, killing everything else except the brassicas. However – under the tunnel arugula and lettuce are still growing. We do expect it to succumb to winter weather eventually, especially once the daytime highs don’t make it above freezing. At that point, we will experiment with some very cold tolerant winter greens like mache and tatsoi. For now – we’re still picking salad from outside!
We used 3/4″ black irrigation tubing (comes in a big roll at hardware stores) and cut it at the proper length to make the supporting arches.
We attached the tubing using conduit holders. (Found in the electrical section of a hardware store.) We screwed the conduit holder into the garden bed wood. We used 2 conduit holders to prevent the tube from wobbling from side to side.
We then cut the greenhouse plastic with some extra on both ends. (We used a roll of 10 ft. wide 6 MIL clear greenhouse film from an ag supply company.) We wrapped the long ends around a metal pipe, and further secured it with a few pieces of lumber. We folded up the short ends and secured them with lumber scraps. It is easy to undo any of the sides to access the greens inside.
The Winter Harvest Handbook: Year-round vegetable production using deep-organic techniques and unheated greenhouses by Eliot Coleman is a great resource if you are interesting in exploring this topic further.