Proper structures can extend growing season

Wednesday, August 1, 2007 | 12:00 a.m. CDT; updated 6:17 a.m. CDT, Tuesday, July 22, 2008

As much as gardeners love to be outside working in their gardens, only a few like the heat and humidity — and insects — of the summer garden here in Missouri. And while there is always great expectation and enthusiasm for gardening as spring springs out, there is also something to be said for fall gardening if one can handle its unique problems.

It is now time to begin planting the fall garden, but it is also too hot for many seeds to sprout. Yet if they don’t sprout soon, their maturity is at hazard to an early frost. Still, some things can be done.

The first thing is to construct a tunnel over your planting row, first to support a covering of shade cloth that, with watering, can keep the soil cool enough for many seeds to sprout, and second, to support a covering of plastic to protect the resulting plants from the first siege of fall’s frosts.

First, buy an inexpensive 10-foot length of rigid plastic plumbing pipe an inch in diameter and cut it into shorter pieces, each 15 to 18 inches in length. These pieces are to be embedded in the soil on opposite sides of your planting row or raised bed, spaced about 2 feet apart on both sides of your planting area. The easiest way to do this is to take a piece of wood, say from a broom handle, and drive it into the soil at each spot where you want to embed a length of pipe. Work the wood around a bit and then withdraw it from the soil. Then drive the plastic pipe into the resulting hole. The pipe only needs to go in for 9 inches or so and the wooden driver only 6 or so inches. All you want is enough depth so that the pipe remains in place.

Then buy a length of flexible black plastic water pipe (it is sold by the foot to whatever length you wish) of a smaller diameter (say ¾ of an inch) than the pipe you embedded. Cut this pipe to a length so that, with each end inserted into the embedded plastic pipe on opposite sides of the row (forming an arch over your row or raised bed), the arch clears the soil by about 2 feet at its peak. If your row is 4-feet wide, a 6- to 7-foot length of such flexible pipe will make a nice arch over the row. I recommend four arches spanning an 8-foot length of row.

With your arches in place over your row, you can drape first shade cloth (available from gardening suppliers), and then, later, clear plastic, over the arches to protect your seeds and plants from extremes of heat and cold, thus extending our Missouri season a useful bit. I have routinely harvested cool weather crops into mid- to late-November this way. There are a number of ways to hold the arch covering to the arch. Clips made expressly for this purpose can be bought, but anything that works for you will do. I use a 2- or 3-inch piece of black pipe from which I have cut out about three-eighths of its circumference and just clamp this piece over the shade cloth or plastic. One should add that plastic pipe can be cut with practically anything that is sharp and can cut heavy cardboard.

So now, when and what to plant under your season-extending arches? Generally one can plant the vegetables of early spring, so long as they grow low to the ground. Among these I include arugula, lettuce, spinach, most mesclun mixes, kale and radish, all of which are quick to mature and can be planted from now into September. You might even try fall cabbage, carrots and turnips, though it is a couple of weeks late now to start these, unless you feel you can rely on the continuing (so far) mild effects of global warming on our Missouri climate. Just this week a friend told me he’d seen a mockingbird on this side of the Missouri River for the first time.

Dennis Sentilles, MU professor emeritus of mathematics, is a Missouri Master Gardener and a member of Katy Trail Slow Food International with a love for working outdoors and eating simply and well every day. He can be reached at

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