With fall definitely in the air, the gardening focus now shifts to harvesting, clean-up, and “putting the garden to bed.” It’s not generally a time to think of planting. Yet with very little effort you can sow a final crop that will work throughout the dormant months to improve your soil’s structure, protect it from erosion, retain vital nutrients, and encourage helpful soil micro-organisms and earthworms, ensuring a rich and healthier planting bed for next year.
These crops are known as soil building cover crops. Sown in September, these fast growing grains and grasses have wide-ranging benefits. Their rapid growth will easily outpace fall weeds. In addition, the topgrowth will hold soil in place, slowing runoff from rain and preventing leaching of soil nutrients. Below ground, extensive roots will take up nitrogen and other nutrients from deep within the ground. These nutrients will then be readily available when the cover crop is turned under in the spring.
Vigorous and extensive root systems also break up compacted soil and increase its porosity by creating the passageways necessary for movement of air and water. And of course, when the crop is incorporated into the soil next spring, it will provide copious amounts of organic matter.
There are three great reasons for growing your own organic matter. It’s easier than making compost, especially if your garden is large. It’s a cleaner source of organic matter than manure, since manure can often contain weed seeds. And it’s far cheaper than buying bagged compost. An inexpensive 500 gram packet of seed will cover a 200 square foot garden and, under optimum growing conditions, has the potential to yield about 25 pounds of organic matter.
Soil builders planted in the fall must be frost hardy, so your best choices are winter wheat and fall rye. Both are easily obtainable from seed catalogues and seed supply stores, and both are easy to plant. Simply broadcast the seed and rake it into the soil. A depth of one to two inches is ideal. Keep the area watered until plants are established. Seeds germinate in about a week and will put on an impressive amount of growth before being slowed by freezing temperatures. Plants are not killed by hard frost, but simply go dormant until warmer temperatures return. As soon as the snow melts, they’ll quickly begin growing again; indeed, while your lawn will still be brown and drab, cover crops will provide a cheerful carpet of green.
Are winter wheat and fall rye interchangeable as soil builders? Yes and no. While both offer great benefits to every garden and soil type, their growth habits and properties do differ somewhat. Winter wheat is fussy about where it grows. It requires fertile soil and good drainage and will not tolerate low pH, whereas fall rye grows well on all soils, from wet and acidic to dry and sandy. Winter wheat is a little less frost hardy than fall rye, so if you can’t get around to sowing your cover crop until later, it is better to opt for fall rye.
While the roots of both are great at taking up and storing soil nitrogen, it’s interesting to note that the nitrogen uptake of wheat is only half that of rye, making rye the better choice in areas where you plan to plant those heavy nitrogen users such as corn.
Winter wheat’s root system is not quite as aggressive as that of fall rye, making winter wheat easier to till or dig into the soil in the spring. Rye’s exuberant growth and aggressive roots will provide more organic matter, but can also prove rather difficult to incorporate in the spring if the crop gets too tall (which it can do with lightning speed!) To avoid problems with fall rye, keep a careful eye on its growth and be sure to turn it under before it exceeds about twelve inches in height.
And finally, fall rye has allelopathic effects; it produces chemicals which inhibit the growth of certain weed seeds such as purslane and pigweed. While this is a benefit, not all gardeners are comfortable with allelopathy, and there is some concern that it might also inhibit the growth of small seeded plants like lettuce and carrots. In areas where these vegetables will be planted, it is probably safer to use winter wheat instead. Allelopathic effects pose no danger to large seeded vegetables or transplants.
In order to allow thorough decomposition, cover crops should be turned under three to four weeks before planting vegetable crops.
Whichever one you choose, it’s well worth finding the time to plant a fall cover crop. Your soil and the earthworms will thank you.