Caterpillar Cover-Up

On Friday night we had a light frost in low-lying areas but we received no damage that we could find. Last week we constructed our first "caterpillar low tunnel" inspired by Eliot Coleman's design. We bought a roll of 3-mil std plastic, 100' by 12' ($27), 20 10' brown 1/2" PVC lengths ($25) anmd 40 2' pieces of precut rebar. For the last hoop on each end we pounded in some 1" pipes and used 3/4" PVC to add some stability. We have standardized our beds at 100' long by 4' wide so the tunnel covers 90' of the bed. The tunnel is about 3 1/2 feet tall and access requires removing a pot and lifting the plastic.

At each end we anchored the plastic with 2 40# building blocks. We filled 40 5 or 10 gallon plastic pots with compost to anchor the plastic along the sides. We anchored one end and unrolled the plastic along the windward side. We then worked down the side, one person pulled the plastic over the hoops and the other set the pots on the one foot of plastic along the edge. Then we anchored the other end and then the remaining side.

With a 10 mph wind with 20 mph gusts, total time spent was about 2 hours which included the time spent filling the pots with compost. Filling was pretty fast -- we laid out the pots in a square and dumped about two bucket loads of compost on top and smoothed it by hand to fill the pots. We decided to use compost because we have a lot of it and when it comes time to take down the tunnels, we can just dump the compost in the beds. I believe that one the materials have been laid out, two people can put up a house in about half an hour and take it down in about the same time.

After about a half hour some of the lee side pots tipped over as the plastic billowed out during a gust of wind. We watered the pots to make them heavier, moved them a bit to the center between the hoops and tilted them some toward the tunnel to make them harder to fall over. There were no more problems, even the next day when the wind reached 20 mph. We'll work on some modifications so the tunnel can withstand about 40 mph gusts and a light snow load. We can add heavier side weights, tie the hoops together with a rope purlin and add some tie-down ropes between the hoops. Our steel-hooped houses have been fine with winds of 60 mph.

This first tunnel covered a bed of late snap beans that are about ready to blossom. It's pretty late in the season so we don't know if they will produce anything before we get a hard freeze. We're going to build two more and cover two beds of summer squash that started producing about two weeks ago.

Anyway, we are pretty happy about results so far! Our fall CSA starts in about three weeks so these tunnels will help ensure we have enough produce for our subscribers.