How to build a caterpillar tunnel


This will be our second year on the Hurricane Hill property. One of our goals this year was to work on season extension now that some infrastructure has been put into place. We decided that a caterpillar could be an economical solution to our challenges. We farm on leased land and don't want to make expensive investments in the property, especially ones that we can't take with us in the future. We finally experienced nice enough weather to put it up this week even despite the light snow cover.

MATERIALS: 1'' PVC, 20 foot lengths - 14 each

5/8'' Rebar, 30'' sections - 28 each

Large carabiners - 28 each

Small carabiners - 28 each

1'' woven strapping - 50 yards

Lashing straps - 2 each

2'' wood stakes or metal T posts - 2 each

4 mil greenhouse plastic - 24' x 150' - 1 each

#6 (3/16”) poly rope - 1000 ft

Sandbags - 30 each

The cost of our tunnel was just under $500 ($0.62/square foot)

The total length of our tunnel is 100' from tip to tip of the end points. We didn't want the end points to run longer then our 100' beds because it would block our harvest lanes, so our actual planting area is about 80' long by 10' wide. You can make your tunnel as long as you want, just add another hoop every 6'.

The first thing we did was measure out our space and pound in the rebar. The first rebar stakes were pounded in 10' from where you want the tip of the point to be. Then, we continued pounding in stakes every 6' until we got to 10' from were we want the far point to be. We pounded in the rebar until only about 12'' was exposed above ground.

Clip the two carabiners together and slip one over each stake. Make sure they are positioned so the little clip will be on the outside of the tunnel. The style of the larger carabiner fits perfectly around the rebar in the smaller side of the clip.

Once the rebar pieces are pounded in and the carabiners are in place, start to put up the hoops. You definitely need two people to accomplish this step. We suggest receiving the pipe the same day you put it up if the weather is old, PVC can crack and break if it's bent when too cold. Start by slipping the pipe over one side of the rebar while your partner walks steadily towards you, bending it into an arch. Slip the other end over the rebar and push down so it meets the ground.

Next, pound in one stake at each end 10' from the end bows. Pound in the stakes so they are at an angle leaning away from the tunnel. In this picture, we used a metal fencing post which was not strong enough. We would recommend a sturdier T post or a 2'' wooden stake.

The purlin strap is next - we got a 50 yd roll of 1'' woven strapping. Take one of the lashing straps and tie a loop in it. Slip the loop over the end stake and slide it to the bottom. Put the end of the 1'' woven strap through the lashing strap and pull it through so you have some excess to pull tight. Test it to make sure you have the strap inserted in the right direction so when you pull on it from the top, it won't slip.

Working with a partner, toss the strap over then under each bow. Make sure the strap is going the same way around each bow so it runs along the top side of the bows (the picture below shows the wrong way for the second bow and the right way for the first bow-it should go over the bow first before going under. ) As you move down the bows, make sure you are pulling tight to keep the tension and that the straps wrap around the bows right in the center. Walk back through the tunnel before tightening down and adjust the straps left or right and the bows vertically so they are upright and level.

Once you get to the far end of the tunnel, slip the end of the purlin strap through the lashing strap on the far stake and pull tight. Go back to the first stake and tighten the purlin strap down as well.