Weymouth, Mass. — Last night I go out the rye seed and started sprinkling it about on the few patches of garden soil that are not filled with still-to-be-picked crops. As harvesting bares other patches of soil, they will be similarly treated.
Cover cropping or green manuring, the process in called, and it's one of the best soil-building, nutrient-holding practices you can undertake in a garden. While it doesn't exactly guarantee the vigorous growth of next season's garden, it will come pretty close.
I have long been an advocate of putting the garden to bed for the winter under a thick mulch of shredded leaves, straw, grass, and the like. I still am; that is, for those areas that are harvested too late for even a cold-tolerant cover crop to be grown.
But good as the mulch of dead materials is for the soil, the living mulch is even better.
This is what a cover crop does for your garden soil:
Its roots bind the soil, preventing erosion during winter storms; the green top provides an insulating blanket that prevents the breakdown of soil structure (it retains its crumbly consistency); and it takes up the readily available soil nutrients that would normally be leached away during fall and winter wet periods and stores them for next year's crops.
Further, when turned under the following spring, green cover crops decay much more readily than dry mulching material.
The roots of cover crops are also the home for exceptionally high numbers of soil bacteria, microorganisms that quickly begin processing nutrients as soon as the soil warms up in the spring, releasing them for rapid plant growth.
Two years ago I learned, during an interview with Don Loveness, a microbiologist from Eden Prairie, Minn., that the root areas of plants are exceptionally rich in bacterial life. Subsequent reading of books on soil science confirms this fact.
Apparently, a thin layer of mucus (jellylike) material surrounds all living roots, and bacterial life is higher in this layer than anywhere else.
Roots decay readily, improving soil structure and building new soil at the same time. One reason for such rich and deep topsoils in the US farm belt is that they have been built-up over eons by the ever-growing and ever-decaying roots of prairie grasses.
An experiment by the O. M. Scott lawn products company showed how readily this soil building takes place. The company placed sod over solid concrete and fed and watered the lawn constantly. The idea was solely to test the company's fertilizer products, but in the process it found that the original 1 1/2 inches of sod had almost doubled in thickness in only a few years by a buildup of soil at the base of the sod that could only come from decaying roots.
Ever since I gained a new appreciation of roots, I've cut down, rather than pulled up, harvested crops. Obviously, root crops don't qualify, but the roots of peas, beans, cabbage, etc., can readily be left to decay and enrich the soil. Many weeds also can be treated this way. And cover crops are a means of greatly increasing the root content of garden soil.
In a large garden there may be space for a season-long program of cover cropping in which certain beds are given over to legumes and other soil-enriching covers for the entire year. If you have that type of space, go to it. A majority of gardeners, however, have small backyards, and cover cropping, involving cold-tolerant grasses, is possible only in the fall.
This year I'm sowing winter rye, but wheat or oats would be similarly acceptable. They can be sown in most Northern regions through September, and later the farther south you go.
Such crops germinate quite readily in the still warm soil and, once up, grow vigorously trough the cool days of fall, going dormant only when the really cold weather strikes. Early in the spring they start growing right along with the crocuses, so that you should have a 6- to 8-inch swath of grass by the time the early peas go in.
Generally, a green manure crop is turned into the soil a week to 10 days before the first crops go in.This allows the bulk of the lush, green crop to decay before germination begins.
As I follow a largely no-dig policy in my garden, I cover the green manure crop with a conventional mulch so that it won't compete with the vegetables. This is how I planted peas, with most satisfying results, two years ago. Narrow strips were cut out of the green manure to form bills in which the peas were sown. The 8-inch-tall grass was then bent over and covered with wet newspapers, which, in turn, were covered with a shredded leaf mulch (the leaves were there as much to hide the newspapers as anything else).
The vigorously growing grass never did break through that mulch except for an isolated blade or two, and the peas grew well, presumably feeding on the decaying roots of the cover crop. In turn, the pea roots were left in the soil, contributing to the well-being of the butternut squash vines which covered the bed all summer long.