Lauterbach: Using 'green manure' can transform your garden beds

Special to The Idaho StatesmanAugust 22, 2013 


Good ground cover could be the key to healthy, productive plants like these strawberries.


I've been gardening in earnest for more than 40 years, and nothing has so transformed my garden's ability to produce food like last winter's cover crop.

Over the years, we've worked into our garden soil many tons of fallen leaves, grass clippings, kitchen waste, tree and shrub trimmings, and spent garden plants. Little by little, the soil has improved.

Using a cover crop prevents rain from compacting the soil or eroding it, blocks weed germination, and is inexpensive and easy compared to some other tactics. In the past, I've covered my beds with fallen shredded leaves and grass clippings, but green manure - another term for cover crops - proved far superior in weed blocking and soil improvement. Strewing and raking in seed took much less time than hauling and spreading mulch would have taken.

I'd heard of green manure for years, but never tried one until last year. Old memories of my master gardener friend Dee Matlock saying her soil was the best it ever had been the year after planting a rye cover crop also stimulated that effort.

Last fall, we planted a bag of Olds brand "Green Manure Seed Mixture" in the garden beds. We didn't plant it as thickly or as early as it should have been planted. It didn't look promising, but it transformed my raised beds.

The seed mixture was about 64 percent winter rye, nearly 20 percent annual ryegrass, 10 percent buckwheat and 5 percent crimson clover. Once it germinated, I saw zero buckwheat, and one small clover plant in one 4-by-17-foot bed, perhaps because we planted late, in cold weather.

Lacking in legumes (i.e., the crimson clover), the mixture of annual grains nevertheless produced thick spreading root masses that lightened the soil and added to its organic matter after we dug in the cover crop in early spring.

Legumes are desirable because they take nitrogen from the atmosphere and fix it in the soil. Some legumes are more efficient at that than others, and their nitrogen transfer is further magnified by using the proper inoculant or root bacteria.

Inoculants for peas and vetches are different than those for beans. These are living ingredients, so must be used soon after purchase.

I have heard that some vetches (legumes) are difficult to eradicate after the winter's cover was turned in. The most difficult one was "common vetch," Vicia sativa. Other vetches available are hairy, purple and lana woolypod vetch, apparently easier to kill. Hairy vetch is hardiest. If planted sufficiently early to be well-developed by cold weather, it may survive below-zero temperatures.

Vetches require use of the pea-vetch inoculants for maximum nitrogen-capture effectiveness. Bountiful Gardens claims vetches break off at ground level in spring, leaving their roots (and nitrogen nodules) in the soil. Thus, you wouldn't have to till or dig them in. Vetches bloom in warm weather, attracting bees.

A legume cover crop not only catches and stores nitrogen to stimulate growth in other plants, but the above-ground parts that we sacrifice in spring either may be used as mulch or added to the compost pile.

Local garden centers sell cover crop mixtures and inoculants. There is excellent comparison information at Just search for "cover crops." They carry many different seeds for this purpose, ranging from beans to peas to forage radishes. Watch for winter hardiness unless you intend to let your garden go fallow in summer and use a summer green manure such as buckwheat.

I'd advise staying away from common vetch or alfalfa since both are difficult to eliminate when you want to plant.

If your soil is tough, unyielding clay, consider planting forage radishes, perhaps with a grain crop and/or legumes. Those radishes grow to more than 12 inches long, and one to three inches in thickness. Left in the soil in spring to decompose, they loosen the clay, leaving behind good organic matter deep in your soil. If you have llamas or a calf, for instance, they can graze on the above-ground greens - that's why they're called "forage radishes."

In spring, you can mow or spade in the remaining plants, or rototill them into the soil. Farms use crimpers and plant among the downed plants, but that requires specialized equipment. And be sure you're planting only annual crops, not perennials.


Tomatoes have taken a beating in the Valley this summer from high temperatures. Cover crops described above wouldn't help, but a fertilizer high in phosphorus and potassium could. We still have more than a month before the average date of first frost, and that may be sufficient time to get tomatoes to a ripe size.

Watch the numbers on fertilizer. One I used a week ago is from Alaska Fish Fertilizer, called Morbloom, rated at 0-10-10. No nitrogen, obviously, but we don't need more foliage now, we need more fruiting, and the phosophorus and potassium in the fertilizer will enable that.

Send questions to or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

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