Choosing a cover crop for the winter can be confusing. Let's sort it out into some easy choices.
What to Plant? Let Nature be your guide.Most meadows and prairies have a mixture of grasses, legumes, and taprooted plants that are able to grow thickly, hold the soil from erosion, prevent compaction, absorb water, and build the soil. The famously fertile topsoils of the Midwest were built by just such assemblages of plants. You can mimic that soil-building synergy in your garden.
Make a mix that includes one from each of these:A grass (grains are grasses) like wheat, rye, or barley. Grasses make the most compost material and the biggest root systems of all the cover crops. They are excellent for saving nitrogen that would otherwise wash away. (Nitrogen is very water-soluble.) You recapture the absorbed nitrogen by composting the grass, turning it under, or using it as mulch. Grasses' huge root systems--a single rye plant can have up to 380 miles of roots--lighten the soil and make compost right in the bed when you cut the tops. We use both short (wheat) and a tall (rye) grasses in our cover crop mix for winter.
A legume, like winter peas, bell beans, vetch, or clover. In our standard winter mix we use one upright legume (bell bean) as well as one vining ground-cover legume (vetch). In an area that will be used for other crops next spring, be sure to plant an annual legume, like vetch, bell beans, or crimson clover. Only use perennial clovers if you are making a pasture, path, lawn, ground cover, or other permanent planting.
A taprooted plant, like fodder radish, California poppy, or ag mustard, to improve water absorption, bring deep-buried minerals to the surface, and open the way for crop roots to follow.
If root-knot nematodes or fungus diseases are a problem for you, include agricultural mustard in the mix. This is the flower, by the way, that turns the pastures and vineyards of Northern California bright yellow in February and March. The photo is of ag mustard in a Sonoma vineyard. The leaves are edible as greens and the seeds can be used to make mustard.
Include a few seeds for plants that draw beneficial insects. For fall try calendula, phacelia (bee's friend), poppies, and chervil. For summer, try fennel, cosmos, cilantro, and coreopsis. All are able to grow in a mixed situation with other plants.
In a smaller bed, in containers, or a front yard, where you don't want tall grasses, choose lower-growing options:Thick-growing, ferny-leaved, groundcover will let water through to the soil, but hold it securely from erosion. We recommend Bee's Friend (Phacelia) for this. It will make a very low carpet of leaves all winter, then send up blooming stalks in April.
Our Decorative Cover Crop Mix will stay at about a foot tall all winter and then grow to 2 feet in spring, while fixing nitrogen and producing several kinds of flowers to delight both you and the beneficial insects that help your garden.
For Permanent Plantings:
If you want to replace lawn, or to create a permanent cover crop--on paths, or in an orchard, for example--use clover. White Dutch is the lowest, most even, and most like a lawn. Red Clover is taller, and makes excellent compost, animal fodder, or mulch when cut. It is a good choice for an orchard, hedgerow, runoff-absorbing buffer, or decorative planting. The best choice for areas that will not get water in the summer, either from rain or irrigation, is birds-foot trefoil, shown at left.
This work by Bountiful Gardens is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.