Gardening Articles: Care :: Soil, Water, & Fertilizer

The Tomato-Vetch Connection (page 3 of 4)

by Jack Ruttle

Start This Fall

Vetch needs to grow for about a month before the very hard frosts (about 22° F) shut down everything in the garden, often around the same time that most deciduous trees are losing their leaves. That means you should plant the vetch one to three weeks before the very first fall frost. You want the plants to get at least four inches tall before they stop growing for the season, though in warmer regions the vetch can keep growing all winter.

Abdul-Baki and Teasdale say that the success of the system depends on using a legume that grows well in your climate to give you the most nitrogen and the biomass you need for weed control and soil fertility. In most places that will mean hairy vetch, which is the most widely adapted winter-hardy legume. It grows quickly in fall, overwinters even in the Far North, and then starts regrowing quickly in the spring. But wherever it's quite warm in the fall when you want to plant (as in parts of zones 9 and 10), other legumes like crimson clover or subterranean clover may do as well or better. Consult your extension agent to confirm which winter legumes have proven themselves in your locale.

After you prepare a seed bed in your future tomato plot, plant the vetch, either by broadcasting or in shallow furrows at the rate of an ounce of seed per 10 square feet. The researchers plant in rows, seven of them across the four-foot-wide bed, or about six inches apart.

The vetch begins to grow again in earnest early the following spring. By the time the weather's warm enough to plant tomatoes, it will be three to four feet tall and beginning to flower. The day before planting tomatoes, use hedge shears or a hand scythe to cut the vetch an inch or two above the ground and lay it in place on the bed. You should end up with a dense mulch that is four to five inches thick. It is important to cut all the vetch and cover the stubble. Stragglers that survive can become tangled in the tomato plants. Plant the tomatoes down the middle of the bed by parting the mulch. Set the plants in place and then tuck the mulch back around them.

Where weekly rainfall is not dependable, it is important to irrigate over the vetch mulch. About 85 percent of the nitrogen in the vetch is in the tops, with the remaining 15 percent in the roots. When cut at the prebloom to bloom stage, vetch is very tender and decays readily, but it cannot rot and release its nutrients without moisture. The researchers lay drip irrigation down the center of the bed on top of the mulch to speed up its decomposition. In gardens, wetting the mulch with a sprinkler of some kind would be ideal. "We are developing a farming system, so we use drip tape, which wets the mulch at individual points," says Dr. Abdul-Baki. Drip emitters that deliver a small spray either in circles or half-circles are available.

The researchers use the stake-and-weave method of training the tomatoes (set a stake every two plants and weave twine back and forth around the stakes and plants). But you can use any tomato training method you like. Enjoy the harvest and the freedom from feeding and weeding that the vetch-mulch method provides. By the end of the season, the mulch will have decayed so much that only traces remain. Some late-season weeds may begin to poke through, but they are easily pulled or cut by hand in the soft soil. Besides, it's almost time to plant vetch again.

Before the first light frosts arrive, prepare to plant more vetch, disturbing the soil as little as possible. Cut the tomato plants and take them to the compost pile. Pull or lightly cultivate to destroy any small weeds. Then plant vetch seed, either in furrows or by broadcasting.

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