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

Undersown Garden Crop

As Coleman's planting of corn undersown with sweet clover shows, gardeners can have their food and soil fertility too.


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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