A MONTH OR SO BEFORE KILLING FROST, the vegetable-garden soil that fed me gets a meal, or at least the promise of one. I sow soil-sustaining cover crops (always from non-GMO, organic seed) as the various food crops are harvested, gradually turning my vegetable beds into mini-fields of winter cereal rye (above) and mammoth red clover for the colder months.
Come spring, several weeks before I plan to plant each area, I’ll cut the grain and legume down or mow them, depending on where they’re located, then turn under the remains—like composting in place, with the foliage and underlying root system decomposing to improve soil texture and fertility.
Cover crops can serve other purposes: Some specialized ones, like various Brassicas, can also provide not just biomass but other benefits like pest and disease control; the subject is much wider than this simple explanation but stated most simply:
- Grasses (like rye, sorghum-sudangrass crosses, and wheat) add organic matter to the soil very effectively (note that I don’t list buckwheat, another great cover crop, here; that rhubarb and sorrel relative is not technically a grass or grain, though we think of it as such because of how we use it food-wise);
- Legumes (clovers, cow and field peas, vetch) with their inherent Nitrogen-fixing capability, provide Nitrogen effectively;
- Brassicas and Mustards (rapeseed or canola; radish; mustard) have proven effective against various nematodes, fungi and insects.
Cover crops—there are varieties for each season and each climate—also serve as a living mulch, protecting the soil from erosion, and thwart other weeds, making the management of fallow garden areas (such as during crop rotations) easier than just standing back and watching undesirable plants take over.
It’s not too late to plant winter rye even here in my cold zone, as it will germinate as low as in the 30s, but I prefer to give it about four frost-free weeks if I can so I just start as the beds come empty. I find that if I wait until the garden’s a blank slate it never happens, so it’s easier to just rake empty areas gently and then broadcast seed. Keeping a bag of each of your chosen cover crops on hand insures you’re always ready, and planting two in combination (normally including one legume; that’s winter rye blades and the just-germinated red clover, above) is another good tactic.
If I had empty areas in spring I might use hairy vetch or oats or field peas here or a convenient pre-packed mixture; in summer, I could use annual ryegrass here or buckwheat, among others. Depending where you live, and what your purpose and timing is, here are some sources of high-quality seed:
PEACEFUL VALLEY, in California, has a good selection for various regions, and a how-to video on cover crops along with other information.
TERRITORIAL SEED, in Oregon, breaks its list down by season;
BOUNTIFUL GARDENS in California calls them “compost crops;”
JOHNNY’S SELECTED SEED in Maine offers many varieties, too.
CORNELL UNIVERSITY has a longer list of sources, many commercial and geared to organic farming, in a series of thorough though technical recent articles.
Gaia’s Garden: a guide to homescale permaculture is a great book and has some great charts about all the different kinds of green manures and what they add to the soil and what kinds of soil they’re good for.
Love using green manures — helps smother out the weeds as well. I regularly use the grasses and legumes, but didn’t know about the brassicas! will have to try. Thanks!
I want to try a cover crop this fall, but I am not sure if I am too late. I live in MN (zone 4). I ordered a compost mix that contains fava, vetch, wheat and rye. Will this work for my area? Also, the fava beans are separate, and I am unclear if I should plant them now or in the spring.
Welcome, AmyD. The University of MN Extension Service has a bulletin on cover crops for your area; favas can be for winter, yes, but I think in extra-cold areas they are sown late summer to get a jump. Have a read. I might be tempted to save them for early spring instead. The vetch and (winter) wheat and rye are perfect; get them in now.
Margaret, do you know if fava beans are among those recommended as cover crops? Seems like I heard that once. Ever tried growing them?
Ooops…I clicked on one of the seed sites and they’re listed right there, plain as day. Anyway…ever tried growing them? I think my Lebanese father might just cry if I showed up for Christmas with fresh fava beans.
When you say you turn them under in spring, do you mean with a roto tiller or can you just do it with a spade or fork?
Welcome, Maggie. Either way; mine are in raised beds, so I use a shovel or fork or both, since the tiller cannot get in there. You will have to kind of chop a bit like you would any clods of old growth you were turning under. Let it decay a bit, then turn again. Hope to see you again.
Thanks for your help! I will get them in the ground today.
It is my understanding that rapeseed (canola) is genetically modified. That is why I don’t buy canola oil. Don’t think I’ll be using that in my garden or in my body. Check your chips and peanut butter too. Like soybeans and Montsano these genetically modified crops are spreading worldwide.