In the spring we built a caterpillar tunnel (read about that here) and it seemed fantastic … until we had a touch of wind (well a big touch). We wound up with collapsed arches, twisted ropes, and plastic sprawled across the leeks, salad greens and a half acre of rye. A disappointing development in our tunnel adventures. I went back to the books looking for hints to what we could change. Then I called Ted Blomgren of Windflower who has been using dozens of caterpillar tunnels for years. I explained our design and what had happened. He recommended a few changes and mentioned how his designs have evolved over time. His advice seemed sound and we followed his recommendation.
These are the key changes we made in our caterpillar tunnel:
- Replace the ground anchors
- Anchor the ends more solidly
- Use wirelock to attach long pieces of plastic
REPLACE THE GROUND ANCHORS
In our original design, we tied the ropes that held the plastic to rebar ground stakes. We replaced 2/3 of these stakes with ground anchors. These ground anchors are screwed in and are more resistance to pulling out. They come in different lengths but we chose 30″ lengths since they were on sale. These anchors are definitely harder to pull out then rebar stakes, but they also take significantly longer to install. If we build additional caterpillar tunnels, I would like to try shorter lengths and see if they are as strong.
ANCHOR THE TUNNEL ENDS MORE SOLIDLY
Initially, when we anchored the the tunnel end, we’d inadvertently left a 4″ space between the ground and the plastic trying to get the plastic tight. Ted Blomgren really stressed the importance of keeping the ends flush with the ground. So we shortened the tunnel by 8 feet to liberate more plastic and bunched it on the ground tying it firmly to a t-stake.
Ted Blomgren also mentioned adding additional weight to the ends to maker sure they don’t lift. This made sense – I think our problem with the first tunnel started when the ends broke free, whipped around a bit, then peeled off the structure and went airborne.
To keep the ends down, we added a number of 20-30lb bags of sand. The folds of the plastic have also since filled water adding significant additional weight.
USE WIRELOCK TO ATTACH LONG PIECES OF PLASTIC
The last comment that Ted Blomgren made was that a single piece of plastic works fine on tunnels 100′ to 150′ long but when he builds longer tunnels he often uses 2 pieces of plastic attached with wirelock to the middle arch of the tunnel. Since our tunnel was 300′ long, I gave this point a lot of thought.
We cut the 300′ piece plastic into 3 pieces and attached them with wirelock to the arches at one third and two thirds the length of the tunnel. Attaching the plastic this way felt noticeably more stable and secure than our first caterpillar try.
DID THESE CHANGES WORK?
We rebuilt the tunnel in early August and 2 months later it is still standing. We have had some pretty strong winds and it didn’t budge. Due to the tunnel being uncovered most of the summer, we didn’t get most of the advantages of covered crops but we’ve picked tomatoes a month later than we usually do. I am excited to start next year with a fully functional and static caterpillar tunnel.
Now, I am waiting for Greta Kryger to knock on my door so we can drive down to Moncton for the organic seed symposium. Perhaps, I will see some of you there!