All About Cover Crops

Infuse your garden soil and plants with nutrients and beneficial microbes with this collection of hardworking, quick-growing, simply amazing cover crops.


| September/October 2015



barley

Barley is helpful for retaining nitrogen in the soil, and it dries into an excellent mulch in spring.

Photo by Fotolia

Growing cover crops is one of the best methods we can employ to bring organic nutrients to our garden soil, yet it’s often not practiced by home gardeners. This is mostly because information on using cover crops is often tailored to farmers, who use tractors to mow down or turn under cover crops. But that doesn’t mean home gardeners should forgo this tried-and-true technique to build healthier soil and plants. When your main tools for taking down plants have wooden handles and you measure your space in feet rather than acres, you simply need a special set of cover crop plants and the right methods for using them.

How Cover Crops Help

A cover crop is any plant grown for the primary purpose of improving soil, as opposed to food or ornamental crops. Since the early 1900s, farmers have used cover crops to restore fertility to worn-out land. In addition to helping bulk up soil with organic matter, cover crops prevent erosion, suppress weeds, and create and cycle soil-borne nutrients using the power of the sun. Recent advances in soil biology have revealed two more ways cover crops can improve soil.

Rhizodeposition offers a special advantage to those working with cover crops. Many plants actually release sugars and other substances through their roots. They are like little solar engines, pumping energy down into the soil. With vigorous cover crop plants, this process goes on much more deeply than you would ever dig—six feet down for oats and rye. If you leave your garden beds bare in winter, you are missing the chance to use cold-hardy crops such as rye and oats to pump up your soil throughout the season, leading to healthier, more biodiverse soil the following spring. Thanks to this release of sugars, the root tips of many plants host colonies of helpful microorganisms, and as the roots move deeper, the microbes follow.

Bio-drilling is what happens when you use a cover crop’s natural talents to “drill” into compacted subsoil. For example, you might grow oilseed or daikon radishes as a cover crop where their spear-shaped roots will stab deep into tight subsoil. Bio-drilling action also takes place when deeply rooted cover crop plants penetrate subsoil and die. The next crop grown can then follow the rooting network mapped out by the cover crop. Maryland researchers were able to track this process using special camera equipment (called a minirhizotron), which took pictures of the interactions between cover crop (canola) and crop plant (soybean) roots. As the canola’s deep roots decomposed, soybean roots followed the trails they blazed in the subsoil. In addition to reduced physical resistance, the soybean roots probably enjoyed better nutrition and the good company of legions of soil-dwelling microcritters, all compliments of the cover crop.

Dozens of plants have special talents as cover crops. If you live in an extremely hot, cold, wet or dry climate, check with your local farm store or state extension service for plant recommendations—especially if you want to use cover crops under high-stress conditions. Also be aware that many cover crop plants can become weedy, so they should almost always be taken down before they set seed.

How to Take Cover Crops Down

One of the only difficulties with cover crops comes when it’s time to take them down, which is why it’s a good idea to start small with your first cover crop plantings. On farms, cover crops are plowed under, but home gardeners must chop them into the soil or pull them out by hand (or assign the task to a flock of pecking poultry). In some ways, pulling plants and then adding them to the compost pile is the best method. Composting cover crop plants may produce a more balanced soil amendment compared with simply chopping the crop residue directly into the soil. You might also want to pull plants rather than chopping in to avoid possible negative reactions between rotting plant residues and the plants you plan to grow. For example, the cover crop known as sudex (a fast-growing sorghum-sudangrass hybrid) produces gargantuan amounts of biomass (leaf, stem and roots), but fresh sudex residue in the soil inhibits the growth of tomatoes, lettuce and broccoli. Oats, wheat and other cover crop plants also produce allelopathic substances that can temporarily hinder the germination and growth of other plants. However, chopping in plant material will also benefit your soil. If you chop in instead of pulling up the plants, simply plan to wait two to three weeks before sowing crop seeds, and any potential interaction problems will disappear.





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