Clover cover crop boosts soil nitrogen

Changing the way we garden isn’t easy. After all, most of us garden the way our elders taught us. They learned from their forebears, who learned from their ancestors. In fact, on the whole, we garden much the same way medieval people gardened – in long, straight rows, or perhaps in long, rectangular raised beds that are easily tended from both sides.

The simplicity and repetition of gardening methodology learned over the centuries is easily ingrained in us. However, two tools, which have eluded some gardeners, are invaluable in any garden, no matter how large or small. They are neither metal nor wooden, neither clawed nor sharp and pointed. Rather, they are management techniques called cover cropping and green manuring.

These techniques can improve your soil and lessen the number of hours you spend fertilizing, irrigating, mulching and weeding. Over time, they may help improve the level of precious organic matter in your soil, and may reduce your dependency on synthetic fertilizer and pesticides.

A cover crop is a stand of plants grown on ground that is in rotation or that is being prepared for future production. Cover crops provide a blanket of living material over otherwise exposed ground, thereby minimizing soil erosion by wind or water. A green manure is a crop grown for its nutritive qualities. Generally speaking, green manures are selected plants sown and grown briefly, then turned into the soil to serve as “food” for the soil for the next crop. Cover crops can double as green manures, if scheduled appropriately.

Wisely planned and carefully planted, various types of cover crops and green manures can control erosion by providing a stable root system which holds soil in place during heavy rains or gusting winds, increase organic matter when tilled into the soil, improve soil fertility by adding nutrients back into the soil and minimize weeding by serving as a living mulch.

Members of the legume (or pea) family are probably the best known and used cover crops and green manures. Of all the legumes, clover – red clover, Dutch white clover, and, where hardy, crimson and berseem clover – is perhaps most popular because of its ease of growth and ability to “fix” nitrogen from the atmosphere into a form that is useable by plants. Seed from clover is usually inoculated with an organism that boosts its natural nitrogen-fixing ability.

Various clovers have different desirable attributes. Red clover is shade tolerant, grows poorly, but often develops powdery mildew during hot, dry weather. It can be sown in spring or in August, and is an excellent living mulch for corn. Dutch white clover has many of the same characteristics but is somewhat easier to till under than red clover. Crimson clover is not winter-hardy in northernmost New England, but provides better competition against weeds than red clover. It grows best in the cool weather of early spring or late fall and is shade tolerant. Berseem clover is variably winter hardy, as well, however, it can withstand heavy mowing should a gardener use the plant as a cover in pathways throughout the garden.

Hairy vetch is a vigorous growing cover crop that is often interseeded with oats and peas if sown in spring or rye if sown in fall. Vetch will grow in a wide range of soil types and is a strong nitrogen fixer. This plant can take time to establish, but once started, large, intertwining leaves provide a good cover through which weeds have difficulty penetrating.

Japanese Millet, sorghum/Sudan grass, oats and annual rye grass are either annual or are not winter-hardy in Maine, and being such, offer the gardener a solid cover crop/green manure selection that will not present problems associated with perennial crops. Although some (mainly clovers) can sometimes become a nuisance if not properly killed during tilling, these non-hardy crops offer the benefits of cover cropping and green manuring with few drawbacks.

Check with your local garden center or farm store, or look in your favorite seed catalog for the availability of cover-crop and green-manure mixtures to sow in your garden this fall.

Diana George Chapin is the NEWS garden columnist. Send horticulture questions to Gardening Questions, RR1, Box 2120, Montville 04941, or e-mail them to dianagc@ctel.net. Selected questions will be answered in future columns. Include name, address and telephone number.