Reinforcing Caterpillar Tunnels

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?

Yes.

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!

15 responses to “Reinforcing Caterpillar Tunnels

  1. Pingback: Building a Caterpillar Tunnel « Going to Seed

  2. I might “borrow” your design next summer to cover our early turnips and radishes with fabric to help keep the root maggots at bay. I like how you use the bags of sand to hold down the plastic…this would work good for us in the summer when it is windy out.

    • I am not a big fan of spring root maggots either.

      The tunnel needn’t be as tall, as wide, or as long as ours. This tunnel can easily be scaled down using 10′ pieces of PVC electrical conduit.

  3. thanks for sharing your experience with this tunnel. This looks like a great option for our first year farm. Where would I find the wirelock that you used? Never heard of it, not sure what it is. Thanks!

    • Hi Amie,

      Wirelock is an aluminum channel used to attach the ends of plastic sheets to a greenhouse structure. You tuck the plastic into the channel and hold it in place by inserting a piece of wiggle wire (a heavy gauge bent wire) into the channel. There are some tutorial pictures on this blog

      Wirelock is available from most greenhouse and nursery suppliers.

      We purchase ours from Corbeil Bigras (corbeilbigras.com) north of Montreal.
      I typed “wirelock greenhouse” into google and came up with a few U.S. sources.

      Good luck!
      Dan

  4. Hey,
    Where did you buy your earth anchors from?
    Thanks.

    • Hi Shannon,

      We bought our earth anchors from Princess Auto. However they were too long. We’re looking for a Canadian source for 18″ anchors. If we don’t find a source, we’ll order from Farmtek in the states.

      If you find a Canadian source, please tell us about it!
      Dan

      • Hey Dan!

        I love this article. I will probably be building my first caterpillar tunnel this fall, in part based on your design.

        Have you finally found a Canadian source for the 18″ ground anchor?

        Thanks!

        Etienne

      • Les Serres Guys Tessier is putting together a Caterpillar Tunnel kit inspired by our tunnels. They are making ground anchors.

        Good luck with the tunnels. They will be great for farming in your area.

        Dan

  5. Hi Dan,
    I’m going to put up a couple of these babies, 14×90, this fall, hoping they’ll hold some fresh greens and root crops through the winter. Thanks for putting your experiences online. It seems like you weathered the collapse with grace.
    My question is about the endwalls. Have you tried to go in and out frequently through those bunched, staked ends with snow on the ground? How easy or difficult was that? I’m trying to decide if it’s worth it to build an actual endwall for one end of each tunnel, or weather that would be a) a waste of money and time or b) structurally unsound.
    I am dealing with moderate snowfall in Massachusetts, USDA zone 7b, if that means anything to you Canadians.
    Keep up the good work!
    Tom Crimer

    • Hi Tom,

      The tunnel I use through the winter has endwalls. I’ve only used caterpillar tunnels as a three season structures and removed the plastic during the winter.

      I have hesitated in moving to a 4-season caterpillar tunnel for access reason. I am not so worried about snow – I usually dig out the endwalls in January and February anyway. I am afraid of the plastic freezing to the ground.

      I have seen a couple farms around in New York State use caterpillar tunnels all winter long with no access problems. But I wonder if their winter is as cold as ours.

      If you want to build a tunnel with an end wall on one side and the opposite end tied to a t-stake, make sure that your end wall is braced solidly enough to resist the tension.

      And don’t forget to put your arches on 4 ft spacing to resist snowloads!

      Good luck,
      Dan

  6. Thanks for sharing. Do you have advice on finding 24′ pipe?

    • Hi Jonathan,

      At first we bought 21′ and 24′ pipe from a plumbing suppliers. More recently we’ve bought them from a greenhouse manufacturer – they often have a lot of pipes in stock.

      Good luck, Dan

  7. Great Idea – but we live in Windy Alberta. We get 110 km winds here. Is there any way they would stand up to winds that strong?

    • Hi Tim,

      That is a lot of wind. I suspect that they might if you anchor them well like I’ve mentioned above. Our strongest winds are in the 90 km range and our tunnels have stood the test. You could start with a 60 to 100ft-long trial tunnel. If it stays anchored, double the length the next year (using two sheets of plastic and wirelock.) If you don’t lose that one, Go for 300 ft long (with 3 pieces of plastic). And if that holds, time to build a whole fleet!

      A 60-100ft tunnel probably costs $1000 or so to build.

      If you do build, keep me posted.I’m really curious about wind resistance and tunnels.

      Dan

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s