The good news for gardeners is that Upstate New York's fertile soil, steady moisture, and relatively stable temperature make for great produce, in spite of its short growing season. Anyone who has ever flown over the Texas Panhandle, for example, knows just how lucky we are. Who could have thought, back in the 1910s when the southern Plains States were homesteaded, that they would ultimately grow their crops only in circles?
While severe drought and extreme heat are rare for growers around here, late Spring frosts sure are reliable. This year, since we're hoping to have salad produce as early as we can get it for our new salad bowl lunches, we are experimenting with growing tunnels.
Rather than “high tunnels,” which are expensive to buy and difficult to relocate, or “low tunnels,” which require a lot of stoop work, we’ve opted for “caterpillar tunnels” of intermediate size. To construct these, we drove rebar stakes in the ground at 6-foot intervals, in two rows 12 feet apart. To form each support arch, we joined two 10’ sections of PVC conduit and slid the ends over the rebar stakes. We then connected the series of arches with a rope purline, secured at either end to a heavy stake. Then a 24-foot-wide sheet of greenhouse plastic was draped over the arches and purline. Between each pair of arches, a rope was strung across the plastic sheet (and secured to stakes on either side). The excess two feet of plastic on either side is secured with rocks. That last step might be difficult in Iowa, but rocks are always close at hand on our “gravel ground.”
In part, we were attracted to tunnels to protect tomato plants from the rain of spores of Phytophthora infestans, which infected all of last year’s tomato plants with “late blight.” But shielding plants from the rain also necessitates irrigation. So down each side of our tunnel, we installed a drip irrigation tube, with 0.5GPH “emitters” at 18” intervals. We transplanted tomatoes at three-foot spacings, interspersed with pepper and basil plants.
Our tunnel isn't heated, but it provides a little insulation against frosts. Not enough, as it turned out. About a quarter of the tomato plants froze, and all the rest of the plants looked pretty shocked by one frost. On a couple subsequent cold nights, we covered plants with buckets or sheets of floating row cover. Another challenge is overheating. While nighttime temperatures in the tunnel are only a few degrees above ambient, daytime temperatures inside can quickly gain a dozen degrees. So we monitor tunnel temperatures frequently, and adjust by rolling up one or both sides. Stepladders and duct tape play supporting roles.
The Arctic Blast that greeted the Griddle’s opening day almost metamorphosed our caterpillar tunnel into a flying beast. We returned from town to see the plastic cover billowing wildly, and even the plastic arches flexing for flight. We used extra lengths of PVC conduit and lots of duct tape to reinforce some of the arches. Then, adding more rocks along the edges, we managed to secure the tunnel to the ground. However, that experience convinced us that our next model should have more rigid support arches. Therefore, Caterpillar II was constructed with arches of 1” galvanized steel conduit, instead of flexible plastic. To bend the conduit, we built a jig, which incorporated some of the sliding door track that had been dismantled from the front of our garage-turned-Catbird Kitchen. While many materials languish for years in the barn, awaiting a new occupation, this door track was recycled in mere months! So we (some of us) feel justified in the many buckets of old parts with which we share our space.
Here are some pictures of the tunnels so you can see just what we're talking about.