As I paged through an older edition of Horticulture magazine I came across a great article, Cover Up by Alice McGowan (and timely for one of my clients) about cover crops and how they can benefit the ornamental and veggie garden alike. Unfortunately, Horticulture doesn’t seem to archive their articles (even for subscribers) online, so if you don’t get the pub, you won’t be able to read the article—unless you go to the library. But I did find a short video that seems to be directly related to the article.
What Are Cover Crops?
Cover crops—known as ‘green manure’—were initially used by farmers (dating back some 2,500 years) to rest a field and improve the soil’s fertility and tilth. In the past century, farmers have moved away from using cover crops in favor of using chemical fertilizers and keeping fields in production all the time. (My note: This practice is destroying our farmland. We can’t take, take, take from the land. We must also give back. That is part of what sustainability is about. –BG)
In a natural ecosystem, plant material would die as part of the plant’s life cycle, falling to the earth, and composting in place, eventually creating nice humus and fertility for the soil. This humus binds together nutrients and water and contributes to good soil structure—which in turn contributes to the earth’s water-holding capacity.
Cover crops are specific plants that grow rapidly and densely and do a good job keeping weeds at bay, holding soil in place, and improving soil structure and/or fertility depending on what crop is being used. They improve tilth in all types of soil—especially in sandy ones. And if you are among those in our area with hard clay soil, it’s interesting that planting a deep-rooted cover crop for 2 consecutive seasons can effectively break up hardpan (that is VERY hard—like a rock—clay).
Uses and When to Plant
Cover crops function as slow-release fertilizers; they combat both wind and water erosion; their roots prevent soil compaction, increase aeration and provide food for microorganisms. They also contribute bio-mass and some cover crops may attract or repel insect pests. And areas covered with this ‘green manure’ generally dries out more quickly in the spring, enabling earlier planting.
Plant cover crops in summer or fall, but if planting in fall, be sure to sow seeds at least 4 weeks before the first hard frost. For us, at this writing, that window has just about closed because for Zone 8 the first hard frost generally occurs between Oct. 30-Nov. 30. The best seed germination occurs between 50° and 60° F.
There are good uses for cover crops in the ornamental landscape as well as in the veggie garden. As previously mentioned, they can help break up clay soil, and improve overly sandy soils as well. I like to recommend their use when doing a large landscape remodel if the homeowner lacks the resources to plant everything immediately. Often, after installing the hardscape many homeowners are massively disappointed with how much weeding they have to do—even if they’ve applied an adequate amount of mulch. Planting a cover crop over large areas they can’t get planted immediately can help out on many levels. And many cover crops are nice looking—not invasive!
Some Popular Cover Crops
Cover crops can be annual or perennial, and come in a range of heights. To choose the right crop for your needs, think about how long you want or need the crop to be in place. If you’re using it in your veggie garden, how long can you spare that bed? Is it just normal crop rotation? If you’re using it in the landscape, the soil problem you are trying to remedy will help you decide which crop to plant.
Some cover crops have ‘allelopathic’ attributes, meaning they release chemicals into the soil that affects the germination, growth, etc. of other plants (like weeds). Fagopyrum esculentum (Buckwheat) is one such plant. Buckwheat also attracts bees which should be a welcome pollinator in everyone’s garden.
- Avena sativa (Oats). Fast-growing and dies over the winter making them a good choice if you want to plant right over (after cutting short) in spring.
- Lolium multiflorum (Rye). A very sturdy crop that is not killed in winter, so needs to be tilled in well before spring planting.
- Sorghum bicolor (Sudan grass). Provides excellent bio-mass because it can be 12′ tall, but it can be too much for those with smaller lots.
- Trifolium pratense (Red clover). A a cool-season short-lived perennial crop that ‘fixes’ nitrogen into the soil once the clover dies. See my previous post about clover.
- Trifolium incarnatum (Crimson clover). This clover is often confused with the clover above. This one has truly red flowers where as Trifolium pratense has more pink to lilac colored blooms. T. pratense is a perennial and can be invasive if not very well managed. T. incarnatum is an annual and not at all invasive if the flowers are not let go to seed.
For more info on cover crops contact your local Extension or Master Gardener Hotline or Territorial Seed Company.