This commentary is by Ron Krupp, author of “The Woodchuck’s Guide to Gardening,” “The Woodchuck Returns to Gardening” and his forthcoming book, “The Woodchuck’s Guide to Ornamentals & Landscape Plants.”
Lots of natural additions can improve the health of your garden — things like cover crops, legumes, grasses, green manure and winter rye.
Here’s a rundown.
Benefits of cover crops: Cover crops can protect the soil from wind and water erosion, suppress weeds, fix atmospheric nitrogen, build soil structure, and reduce insect pests.
A thick stand of a cover crop protects the soil surface from wind erosion and the cover crop’s roots can hold soil in place against water erosion during heavy downpours. Cover crops left in place for part or all of a growing season can suppress annual and some perennial weeds.
Among the grasses, annual rye has allopathic properties that prevent weed seeds from germinating and suppress weed seedlings around the root zone of the rye.
Legumes: Legumes like peas and beans will take nitrogen out of the air and store it in their plant tissues via nodules on the roots of the legume. Some of this nitrogen is available as roots die, but the majority becomes available when the legume is tilled under (green manure).
The legumes as a group have a higher protein, calcium and carotene content than grasses. They can furnish an adequate supply of most vitamins with the exception of vitamins D and B12.
Alfalfa, sweet clover, red clover and vetch are legumes. They are used for rotations in farm fields with grasses like timothy. Sometimes gardeners use these rotations.
Oats and field peas are another combination of grasses and legumes. Another combination for longer rotations of a year or two include winter rye and winter peas or a rye/vetch mixture. Vetch is hardier than winter peas and winter rye is extremely hardy. A long-term green manure rotation includes perennial grasses such as timothy and perennial legumes such as clover. Another example could be red or white clover included with a hardy grass like timothy for a two- to three-year rotation.
Grasses: Perennial grasses such as orchard grass, fescue, timothy and brome grass, while not as high in quality as the legumes, should be used in mixtures with them. Mixtures of grass-legume have performed as well as legumes alone and have the advantages of increasing total yields, providing a superior sod, and reducing the risk of losing the legumes through heaving and stress kill.
Sudan grass, Sorghum-Sudan crosses and small grains may also be used in mixes. Most of these grasses are used on farmland, not in gardens. Rape is neither a grass nor a legume and is used with some grass/legume combinations. This plant of the mustard family is grown for its seeds, which yield canola, or rapeseed. Plant roots exude a sticky substance that glues soil particles together, creating structure. Grasses are exceptional in their ability to do this.
Soil fertility: Green manuring enhances soil fertility and soil structure by feeding soil organisms and gluing together soil particles into aggregates. When fresh plant material decomposes in the soil, its carbon-to-nitrogen ratio becomes low, allowing the nitrogen to be easily released into the soil chemistry by bacteria. Nitrogen accumulation is greater with legumes, which have nitrogen-fixing Rhizobium bacteria growing in nodules on the legume roots.
Winter rye: Winter rye is an excellent winter cover crop because it rapidly produces a ground cover that holds soil in place against the forces of wind and water. Rye’s deep roots help prevent compaction in annually tilled fields, and because its roots are quite extensive, rye also has a positive effect on soil tilth.
Winter rye will not be damaged by winter’s cold and snow. If you plant it in September, it will continue to grow until December and will start up again in the spring. When sown in late fall, around the time of the first light frost, winter rye is still able to put on just enough growth to provide some protection against soil erosion over the winter.
The problem for gardeners is that if it grows too much — 6 inches to a foot — it will be difficult to till in or turn over by hand because of its large mass of leaves and roots. Also, winter rye has qualities that inhibit the growth of young garden plants in the spring. In this case, you need to work it into the soil for over a month before planting summer garden crops.
It’s probably best to plant winter rye well into October so it doesn’t grow that much and will be easy to till in — in the spring. The key is to work it into the soil as early as you can. A couple of years ago, I let it grow into a grain, which is quite lovely. I mixed in some vetch seed with winter rye, which has a pretty purple color and adds nitrogen to the soil.
A great gardener, Will Bonsall of Maine — an expert on cover crops, grains and seed-saving — says that gardeners need to remember that all green manures are not equal; each is suitable for particular times and situations. For example, gardeners rarely include buckwheat among their garden crops, except occasionally as a green manure. For soil that already has a modicum of fertility, other green manures — oats, for example — give a better return on investment. Buckwheat is not cold-hardy as compared to oats and annual rye.
Buckwheat has a more specialized role — for example, when soil fertility, especially humus, is very low (so that in effect you have very little to invest); when certain minerals, particularly phosphorus, are low; or when an intractable weed problem, such as quack grass, needs to be smothered. In other words, it grabs up water and minerals such as phosphorous and starves out weeds. The bees also love buckwheat. If you have enough growing, you can hear their humming. This always makes me stop and listen and brings me peace. Given somewhat better soil, Japanese millet is a bodacious maker of biomass, but it too is frost-tender like buckwheat.
Bonsall’s favorite cover crop is oats, not the hull-less type he grows for eating. He says, “Oats are very cold-hardy, so I can grow them as soon as the snow goes or a few weeks before it returns, or anytime in between. They grow quickly, and I can sow them, and I can get at least three crops a year, turning them in before they turn to seed. If it grows too tall, I may scythe the bulk of it for compost.”
Oats will survive a few frosts but not the winter. I’ve grown oats many times and have found it is easy to turn into the soil in spring, as it has died back and broken down.
Bonsall says green manures aren’t always grasses and legumes. Some folks plant mustard, the residues of which can eradicate many fungal soil diseases. He said, “Some of the plants we usually curse as weeds can give great service by delving down and bringing up minerals from the subsoil, minerals that would otherwise be inaccessible to our shallow-rooted crop plants. Yellow dock, dandelion and chicory are good examples. Deliberately sow them in rotation mixes, to complement the others. I just don’t buy them; I collect my own seed before mowing.” Will Bonsall lives in Industry, Maine, where he directs Scattered Project, a seed-saving enterprise.
Tatiana Schreiber of southern Vermont says that for years she has been growing her tomatoes in a living mulch of hairy vetch. As the vetch grows, she cuts it down with a hand scythe and leaves the dead vetch on top of the bed to decompose. She says you don’t want to plant vetch too thickly or it may end up overwhelming the tomatoes. At the same time, this living mulch prevents disease-causing organisms in the soil from splashing up onto the plants, prevents soil erosion and loss of nutrients, and enhances water infiltration into the soil.
Tatiana says other crops that can be used as “living mulches” are oats and annual crimson clover. She has had success undersowing brassica with oats, cutting it down as it grows and leaving it to decompose, and undersowing crimson clover with squash. Later in the summer, the clover blooms with beautiful crimson spikes, providing nectar for bees and looking good.
Organic matter: Growing cover crops can help build or maintain soil organic matter. However, best results are achieved if growing cover crops is combined with tillage reduction and erosion control measures. A good supply of soil organic matter is beneficial in crop or forage production. Consider the benefits of this valuable resource and how you can manage your operation to build, or at least maintain, the organic matter in your soil.
Resources: Rodale Institute’s Organic crop consultants and crop rotation. If you have questions, contact consulting@rodaleinstitute.org or 610-683-1416.
Two books: “Organic No-till Farming” by Jeff Moyer or “Dirt to Soil” by Gabe Brown can also be helpful in planning crop rotations.
