High Tunnel Time

March 15, 2015

After a full week of when daytime highs rose well above forty degrees and nighttime lows remained above freezing there is quite a bit of muddy green showing in the Michigan landscape this morning. There is also still a fair amount of snow in my yard. I doubt that the areas along the curb where it was piled high from shoveling will be clear even by tomorrow night, despite the predicted high for 2015 at 66°. Diane was out at Appleschram Orchard yesterday attending to the hoophouse where the early season pickings for Thornapple CSA will very soon be enjoying the convection-warmed air. Maybe I should take a week off from this season’s musings on food and culture to say just a word about the hoophouse.

First a note on terminology. I’m sure all the hipsters among my readers already know it, but we have some great new words to toss around over our pumpkin spice macchiato these days. Like, “Did you see that high tunnel going up on the North Farm above Chatham?” I could spin off a tangent here by explaining how I can be so sure that every enumerable hipster among my devoted audience of readers knows this, but I’ll resist the temptation for epistemological diversions. Both of my regular readers can probably fill in these details for themselves.

A “high tunnel” is a kind of hoophouse. A hoophouse is a kind of greenhouse, specifically one constructed by placing a row of metal hoops in the ground and then covering them with plastic. Generally speaking, a high tunnel is a hoophouse that is tall enough to stand up and work in. Low tunnels—hipsters may know them as “quick hoops”—are placed over plants to produce a little early season warming and to keep the frost off. They get taken off when the danger of freezing temperature is safely past. High tunnels are more permanent fixtures, though there are some very fancy ones mounted on wheels that can be rolled back to give the plants inside the full benefit of summer sunshine. You can also peel the plastic back off of a regular high tunnel, but that’s a lot of trouble. It’s not something you are likely to see at Thornapple CSA’s farm.

Hoophouses have revolutionized the production of vegetables for local markets, especially in Northern climes. By this time of year the late winter sun comes through and warms the air inside, creating an internal convection inside the tunnel that can add 15-20° to the outside temperature. This is not a big deal on days when it does reach 66°, but that doesn’t happen every day of the week in March (or April, for that matter). Nor does it happen every day in October and November. The extra warming is big on days when it fails to crack 40°, and huge when that late March snow comes in and it’s 22° at 9:00 in the morning. And, obviously, the physical barrier of the plastic is important for just keeping the snow off of the tender plants during their early season moments of vulnerability—something working for low tunnels, too. It’s less clear that you get a lot of protection from insects and plant diseases, but there is a shield that works as a first line of defense.

The hoophouse is one of the reasons why it is just fallacious to suggest that organic and local production is a nostalgic return to the farm production of yesteryear. Next time you are down at the coffee bar, try using the term “high tunnel” very casually in a conversation. If you are very ambitious, you can explain the bit about fallacious inferences too. Just remember that ‘fallacious’ rhymes with salacious, and be prepared for someone to take it the wrong way.

Paul B. Thompson holds the W.K. Kellogg Professorship in Agricultural, Food and Community Ethics at Michigan State University

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