Growing Green Manure: A Fertilizer from the Garden

Grow food and cover crops at the same time with a technique called undersowing.

| September/October 1989

Eliot Coleman, farm manageof MiltoAcademy's Mountain School Program in Vermonthas been a leading practitioner of organic growing for 20 yearsThifall bringthpublication of his first book, The New Organic Grower—a treatise of grow­ing techniquethat's thbest market­-gardening guide we've seen in manyearColeman's book hamuch useful information that can be adapteto home gardens as well, such as the following excerpt on innovative ways to combinboth soil-building and edible crops. 

Not all crops are for sale. Green manure crops are grown not for cash but to contribute to the care and feeding of the soil. A green-manure crop in­corporated into the soil improves fertility, but the eventual benefits are even greater.

Green-manure crops help protect against erosion, retain nutrients that might otherwise be leached from the soil, suppress the ger­mination and growth of weeds, cycle nutrients from the lower to the upper layers of the soil, and—in the case of legumes—­leave to the following crop a considerable quantity of nitrogen. Other contributions of a green manure are improved soil structure, additional organic matter, enhanced drought tolerance and increased nutrient availability.

The value of green manures has been ap­preciated since the earliest days of agricul­ture, yet the full potential of green-manure use is still underappreciated and unexploit­ed. Growing green manures has traditional­ly been viewed as an either-or situation. You grew either a paying crop or a green manure. If the use of green manures means replacing a cash crop, then the lack of interest in them is understandable. However, there are other options.

There are three ways in which green­-manure crops can be managed: as overwinter crops, main crops and undersown crops.

First, they can be sown for overwintering after a market crop has been harvested. For example, a leguminous green manure could be sown after pea harvest and would occupy the ground until it was tilled in the follow­ing spring. The benefit from a wintered-over legume that provides ideal growing condi­tions for next year's crop is a strong incen­tive for growing it.

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