Low Tunnel Season Extenders

The low tunnel with sides vented open

I'm so excited about my new low tunnels, a small inexpensive version of a green house or hoop house. They'll serve dual purposes: warming the beds on cool nights and either warming or cooling during the day, depending on which crops they cover. The greens and peas will be kept cooler by opening up the side of the tunnels to vent out the heat and shaded by the 85% light transmission of the fabric. Tomatoes, cucumbers, and peppers will be kept warm day and night by venting the sides less.

The baby lettuce and spinach crop should be ready for the 1st farmers' market of the season

The key ingredient was purchasing a 250' roll of 83" wide (almost 7') row cover fabric called Agribon 19. The extremely light synthetic fabric lets light, water, and air through to the plants but does retain enough heat to provide 4 degrees of frost protection on cold nights. To build a 25' low tunnel I used 3/4" plastic PVC pipes spaced at 30" (10 pipes covers 25' and costs around $18. The pipes are bent and fastened to wooden poles (with electrical conduit straps)that run the length of the bed. Once my pipes retain some of their bent shape with time, I may try the more traditional method of inserting the ends of the PVC into pre-drilled holes in the soil. The fabric is then spread over the frame and the two ends are pulled tight and fastened with rope to a deeply driven stake. At this point the fabric will hold it's place (vented open or closed) in up to moderate wind. But we don't get just moderate wind around here so I'm going to run a piece of string or cord over each hoop, trapping the fabric between the string and the pipe. Sandbags will also be used to weight the fabric down when needed. On days when extreme wind is forecast, I'll just slide the fabric completely to one side of the hoops, and bunch it up against the ground with a heavy weight on the top; why fight the wind with nearly transparent fabric. The final cost for each tunnel breaks down this way: fabric $6; pipes $18; pipe fasteners $3; string and screws $3.