Putting up the caterpillars 6


PVC pipe

On April 21st, we hosted a work-party to help erect our two caterpillar tunnels. Much like a greenhouse, these structures will provide a sheltered, warmer growing environment for various crops, but there are a few important differences between these two types of structures. Caterpillar tunnels are a) less expensive, b) simpler and faster to construct, and c) easily moved from one location to another in the field.

There is no one way to build these structures. The design for our tunnels was inspired by Ted Blomgren from Windflower Farm in NY. We also sought inspiration from the construction of the caterpillar tunnels at La Ferme Cooperative Tourne-Sol, which are well documented in a number of blog posts by Daniel Brisebois.

After some preliminary ground prep – Bryan had disced and rototilled – we squared the site of each tunnel.

We pounded in 2ft tamarack ground-stakes every 4ft along the two lengths of each tunnel area. The dimensions of one finished tunnel are 12ft by 132ft.

larch posts

Next, we fitted 20ft PVC pipes over the wooden ground-stakes, creating arches.

hoops

Then we inserted Duckbill ground-anchors 4 inches away from the structure at the base of every arch, on both sides of the tunnel. The purpose of the ground anchors is to fasten the ropes that tie down the plastic on the structure. Two different sizes were used: the larger ones secure the ends of the ropes, and the smaller ones act like belt-loops with ropes travelling through them freely. At the ends of each tunnel, where we wanted extra strength, we alternated between larger and smaller ground-anchors. For the majority of the tunnel’s length, however, larger anchors were placed only at every fourth arch.

Then, with the help of our entire work-party (7 of us in total) we simultaneously unrolled the plastic and pulled it over the arches working end-to-end. We were careful to drape the plastic symmetrically, distributing plastic excesses equally.

caterpillar

Next, starting at one end, we bunched and tied the remaining plastic together, and anchored it to a metal T-stake that had been driven into the ground at a 45 degree angle pointing away from the structure.

endstunnelssecuring plastic

Then from the other end, we pulled the plastic along the structure as tight as we could, and then repeated the anchoring process at that end.

Then came the ropes. Starting at one end of the tunnel, we tied ropes to the large anchors on each side, and then criss-crossed them across the structure until they reached the next large anchors.

ground anchorsduckbill anchors

For additional wind-bracing at the tunnel ends, we secured a rope about waist-high on both sides of the third arch from the end, looped it around the remaining two arches, and tied it to the T-post.

Entry into the tunnels from the sides is also working as hoped: by pushing/scrunching up the plastic, the tension between the ropes and arches hold it up. We think the criss-crossing set-up of the ropes, combined with having the anchors at the base of the arches are making this effective.

caterpillarplastic

It’s been five days. The tunnels are still standing, and they’ve had to deal with some pretty windy conditions!

We’d like to thank Carrot Cache for their grant to purchase the materials to put up these caterpillar tunnels so we can extend our growing season! They are amazing supporters of sustainable food production! They also sponsored a great webinar on season-extension structures: http://www.agriwebinar.com/Preview.aspx?id=c108943b-633b-461a-8950-389648ff4740

work party

Our costs and suppliers list can be found here: Costs and Suppliers

 


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6 thoughts on “Putting up the caterpillars

  • Adam Lemieux

    I’ve been inside one of Ted’s tunnels in the middle of the winter with a foot of snow on top of it. It’s a great design. Very strong. The nice thing about this design is that you can rotate uncover the tunnle and rotate the hoops 90 degrees to allow reworking the soil with a tractor. I also like how you showed the costs and where to get the materials. Very cool. $0.83 per square foot is hard to beat.

    Nice work on your tunnels. 🙂

    Adam.

  • Dan

    These look great.

    I like how you don’t have a ridgeline on your tunnels. I’m curious whether the crisscrossed ropes will manage to keep the plastic open year round. If so, maybe we’ll give that a try. Anything to make things simpler.

    Look forward to seeing the tunnels in person.

    Dan

  • Sarah

    Good job!
    How is this tunnel holding up? We built one very similar, but without ground anchors and have seriously struggled with it. I’m very interested in how yours has endured!

    • broadforkfarm Post author

      Ours is holding up great! We’ve had no issues with it at all and its endured really well in windy conditions. Can’t complain at all about it.

  • mahendar

    Dear sir,
    This is mahendar from India, i have 5 acres of green house in India. i would like to do an experiment with cater pillar tunnel. please let me know the dia, thickness & length of the plastic pipe & please let me know the foundation measurements.

    it will be very useful for my experiment, if you give me the above details….,
    thanks & regards
    good day

  • yvonne vaughan

    We are new growers, and I have done a lot of reading on caterpillar tunnels. We are building one, but in the process of ordering the plastic, I came across a disclamer on Johnny’s seeds that they don’t recommend letting the polyethylene plastic come into contact with the pvc, as the chemical reaction will degrade the plastic. I wondered if you could tell me if you are having any trouble with this? The customer service lady told me growers who use pvc are possibly painting the pipe with white latex or uv protective paint, or are using plastic they know will wear our after a season, or are using four year plastic knowing it will not last as long with the pvc as opposed to metal hoops. I would so appreciate any comments you may have on this. Thank you, Yvonne