The Benefits of Building a High Tunnel

Enlarge Image Image Gallery High tunnels like this one shelter plants from pests and extremes, allowing for higher yields. George DeVault

Rain is pouring down — again. We’re already some 23 inches above average precipitation on the year, and it’s only September. However, my crops and I are nice and dry, thanks to the largest of the four high tunnels I built on our small farm in southeastern Pennsylvania.

What’s a high tunnel? It’s a poor man’s greenhouse. Instead of expensive glass and intricate steelwork, the structure consists of a simple frame — usually made of bent galvanized metal pipe or PVC pipe, though wood can be used. The pipes that form the “bows” or “ribs” of the frame fit into slightly larger diameter pipes that are driven two or three feet into the ground to form the foundation. Smaller PVC pipe is sometimes slipped over pieces of rebar hammered into the ground. The whole thing is then bolted together with baseboards, purlins, end-framing and doors to meet your needs.

The frames are covered with one layer of 6-mil UV-resistant greenhouse plastic. The plastic is attached with everything from expensive aluminum channels and “wiggle wire” to wooden lath, old fire hose, strips of inner tube, and even used drip-irrigation tape. The tunnels are not heated, but having an emergency heat source handy is cheap insurance for protection from extreme cold snaps, heavy ice or snow.

Whether you’re a backyard gardener, a market gardener or a commercial grower, you can build a high tunnel to meet your needs in just a couple of days using simple hand and power tools.

Benefits of building a high tunnel

The “high” part of the name means that the tunnel is high enough that you can stand up straight inside. “High tunnel” is a somewhat loose term. It includes everything from tall, Gothic arch structures to Quonset-style “hoop” houses, which also are known as cold frames. In tunnels with high sidewalls, there is plenty of room to operate garden tillers and even small tractors with tillers, mulch layers and bed shapers.

In extreme heat, the plastic skin can be easily shrouded in, or even replaced with, shade cloth. Add drip irrigation, minisprinklers and maybe a fan or two, and crops inside the tunnel will be almost as cool as veggies in the supermarket produce case.