Every gardener should know that soil is the key to a healthy, productive garden.
Gardeners spend millions of dollars every year buying soil, peat moss, composted products and biostimulants to improve their soil. Some of us even produce our own compost (gardener’s gold), though there never seems to be enough. Unfortunately, few gardeners use cover crops—one of the least expensive and most efficient ways of building better soil—which is sometimes referred to as “adding biomass.”
Now it’s still summer and you may think it a bit premature to discuss cover crops, but good stewards of the soil can make use of cover crops from the last frost of March to the first frost of November then right through the winter. This year we actually took a large vegetable garden out of production and we’ve just sown our third cover crop on it this season. Having given this plot a rest, while at the same time rebuilding the soil, next year we’ll get a fantastic garden out of it using less fertilizer.
Cover is imperative where various crops in other vegetable gardens are finishing, or for gardens that are only in the planning stages for next year and are not being used. And it’s not just in home gardens—cover crops are being used at orchards and vineyards where seeds are sown between rows of vines or trees for soil enrichment, erosion and weed control.
At this point we need to make a technical differentiation. Another term that is used interchangeably with cover crops is “green manure.” But, to some, green manures are planted during the growing season while cover crops are used between growing seasons.
More recently, cover crops have been used to hold the soil while green manures are used to enrich it. Some crops do both.
For early sowings, from mid-May through late July you can consider soybeans planted at 2 to 3 pounds per 1,000 square feet. This legume will produce its own nitrogen, though it is rarely used by home gardeners.
Buckwheat and oats are non-legumes that can also be used from spring through late summer, at the same rate. Oats are a very fast growing summer crop that provide quick cover. Buckwheat, on the other hand, needs to mature prior to frost so it can be tilled into the soil.
In late summer you can use red or white clover or legumes, such as hairy vetch, which will provide good amounts of nitrogen. Be careful with the clovers though, because they may come back to haunt you next year if not properly turned under.
Most gardeners remark that they don’t want to give up precious time and space during the growing season for these valuable plants, or they shun the work involved with turning the cover crop into the soil. Both of these factors can be avoided by choosing to grow a later planting of winter wheat or winter rye and turning it into your soil in early spring. This utilizes space that’s presently unused, unproductive and prone to collect weeds.
But for those of us who always forget until the last days of September or October, only the wheat and rye mentioned above will work. And don’t make the mistake of planting turf-type perennial rye—it’s really tough to get rid of once established.
Planted September through October, annual rye seed produces grass-like plants with blades that are thicker, wider and taller than lawn grasses. Unlike lawn grasses, they are annual plants. This means that they will decompose when turned into the soil and not regrow like common turf grasses. They make ideal choices for vegetable and flower beds, which are replanted each year.
Both winter wheat and rye (do NOT, repeat do NOT use perennial rye) can be slowly sown throughout your garden until two weeks before the soil freezes, which out here can be as late as mid-December. An unexpected earlier freeze will just delay germination.
This gives the gardener a lot of flexibility. You can choose to prepare the garden and plant your cover crops all at once or plant only in empty rows, around plants or in other spots as they become available.
The amount of organic matter these plants will grow for you will vary with how long you want to grow them into next spring. The longer they grow, the larger the roots and tops and hence the more organic matter available to be turned into your garden.
Of course there are a few factors to consider.
The larger the plants the more difficult to turn the soil, unless you first cut it down with a weed trimmer or mower. In fact, if you want to experiment and just let these plants grow to maturity and produce seed, you will produce very attractive wheat or rye plants.
Unfortunately, at about that point you’ll be wanting to plant tomatoes, peppers and eggplants. If you let it grow and grow, you own cover crop would be too large to incorporate into the soil with the equipment that most of us have access to.
There are benefits—beyond producing organic matter—that are part of late season cover crops. These crops cover your garden throughout a part of the season when the winds out here can be relentless with rain and melting snow helping to erode away topsoil and leach minerals. In fact, many localities require farmers to plant cover crops within a certain time after harvest to prevent erosion, blowing dust and topsoil depletion.
The root structure of these plants produces aggregates or clumps in the soil, increasing soil pore space and tilth, both very valuable aspects of a healthy garden. Tilth and pore space enhance populations of valuable soil microbes, earthworms and other animals, which are a part of the growing environment. Therefore, if you choose to turn your cover crops into your soil very early in spring, before they produce a lot of top growth, you are still greatly improving the health of your soil.
You don’t need much seed to cover your garden. In fact, 2½ to 3 pounds of wheat or rye seed per 1,000 square feet (4 ounces per 100 square feet) of garden space will be sufficient.
Broadcast your seed over a soil that has been cultivated to 2 to 3 inches. Cover lightly with soil by raking gently in with a metal garden rake, not a fan rake, then use the rake head to pat down the loosened, seeded ground. Or use a very light (empty) roller for larger areas.
Most of the cover crops and green manures that I’ve mentioned can be found at larger, local full-service garden centers, farm suppliers and a number of mail-order garden suppliers. Cornell has a good fact sheet with a helpful chart on the topic at covercrops.cals.cornell.edu.
So cover those empty areas and put them to good use. Resist the late summer urge to just let the vegetable garden go to sleep. Plant a cover crop and do your part to pay your soil back for its hard work. And, as always, keep growing.