A cover crop is a crop you grow for the soil, instead of for your plate. The practice of growing specific crops just for fertilizing and building the soil dates back to the Roman Empire.
Cover crops add organic matter to the soil, and add nitrogen in a slow-release way that plants can handle, leading to less nitrogen volatilization (read: waste!). Cover crops can also act as mulches if managed correctly, improve soil physical properties in just one growing season, and attract beneficial insects and pollinators to your garden. They are also beautiful!
While you’re thinking about those plentiful reasons to consider cover cropping, also think about maximizing solar energy in your garden. Think about how every inch of soil that is covered with plants means an inch of active conversion of solar energy into energy that is usable by YOU, via your garden crops that benefit from healthier soil. The alternative is bare soil, and we know what that means: WEEDS, and LOSS OF NUTRIENTS AND TOPSOIL via erosion and volatilization. Cover crops can be seeded in just one bed, or they can be grown in entire sections of your garden. In short, they go in wherever you have time and space.
- When cover cropping for long periods of time, combine a small grain (think cereal ingredients like oats, barley, rye) and a legume (nitrogen-fixing plant like peas or vetch) for best results.
- When cover cropping for shorter periods of time, consider green manure crops, or tender, quick-growing crops that will outcompete weeds and, when finished, will provide some easily-digested, supple foodstuff for the soil microorganisms. Examples include buckwheat and field peas.
When deciding what to grow, always consider the following:
- What is the crop time? Figure out how long it will take your cover crop to mature from the time you seed it to the time you kill it. The trick to getting the maximum benefit of cover crops is to allow the crop to get as mature as possible without making seeds. When the time comes that you can let it go no further, you kill it, allowing it to provide a layer of mulch on the soil, which feeds the soil food web below as it decomposes.
- How will you kill the cover crop? There are a variety of methods for killing a cover, but the most popular for home gardeners is mowing, weedeating, or just chopping down with some loppers. However, make sure you’re working with a cover crop that will die from mowing, otherwise you’ll end up with a regenerating cover, which may not be what you’re after. For example, winter annual rye will only die-by-mowing after it creates a seed head, but before it releases its seeds. Austrian winter peas, on the other hand, can be mowed anytime and will die.
- How long will it take the cover crop residue to decompose? Residue that is tender, like buckwheat or peas, will be assimilated by the soil critters much faster than sorghum stalks or barley stems. This is important based on what you plan to do with that bed after cover cropping. Do you want to kill the cover crop and plant seeds as soon as possible? If so, consider a tender cover like buckwheat. Do you instead want to kill the cover crop and have its residue provide mulch on the soil for as long as possible? If that’s the case, sturdier, carbon-rich crops like oats or sorghum are great options.
- What is the season? Some cover crops are best for summer, like cowpeas, soybeans, and sorghum-sudangrass hybrids, whereas there are other specific cover crop options for wintertime, such as winter wheat, clovers, and Austrian peas.
- What is the subsequent food crop? Knowing what you want to grow after the cover crop is done will help you select the best cover crop species. For example, if you plan to grow a high-feeder (a crop that pulls a lot of nutrients from the soil), like tomatoes, it’s a great idea to precede the tomato crop with a leguminous cover crop like field peas or clover, which will add nitrogen to your soil. On the other hand, some cover crops can have negative effects on the food crop you plan to plant. Winter rye residue is allelopathic (releasing toxic chemicals as it decomposes) to seeds of certain brassica species. If you are prepping soil for your spring cole crops and are planting from seed, consider a different cereal grain like wheat, instead.
In many ways, cover cropping may seem like a practice for the super advanced gardener only, because it involves having a good grasp on your crop rotation, and knowledge of how to harness the positive biological contributions of specific species for the benefit of the garden as a whole. Although cover cropping seems intimidating at first, you can ease your way into the practice. You’ll be amazed at how much you learn as you go!
- One great place to start is with buckwheat in your summer garden. Simply pick up a bag of buckwheat seed locally (link to resources), and plan to hand-sow it in your empty garden beds during the summer only. Watch it carefully, and when the white flowers start to pop open, it’s time to mow, weed eat, or clip it down. Fork the mowed residue into the soil and voila! You’re off to a great start on your cover cropping adventure.
- Use cover crops to let your garden rest over the winter. Select a winterfriendly legume and a cereal grain (hairy vetch and winter rye, for example, or winter wheat and crimson clover). Sow them in late summer according to the directions from the seed supplier, and let them grow all winter. They’ll go dormant for a period during the coldest months, but come spring, they will shoot up in a display of lush green goodness that your soil (and your soul) will admire. When they mature in early spring, kill them, till them in, and get started with your spring crops.
A handy tool when tackling best cover cropping practices is a good book that addresses all the different species available, their function, how to grow them, and how to kill them. A book often used is Building Soil for Better Crops by Fred Magdoff and Harold Van Es. The book covers several topics for building soil, including composting, crop rotations, and reduced tillage, but the chapter on cover cropping is accessible and succinct, and provides great suggestions of cover crop species.
Below is a list of common cover crops for gardeners, their season, and their benefits in the garden.