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New Mexico State University

New Mexico State University

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Time to Apply Compost to Home Vegetable Garden

LAS CRUCES--Late winter is a good time to prepare to soil for this year's backyard vegetable garden. The easiest way to bring life back to worn out soil is with a liberal application of compost.

"Finished compost is often called humus," said George Dickerson, horticulture specialist with New Mexico State University's Cooperative Extension Service. "The dark-colored, amorphous structure of compost makes it difficult to determine the organic wastes used in the composting process, whether in backyard compost or municipal compost."

Compost improves the soil structure of the garden. Soils vary from sandy to heavy clay. Mixtures are called loams. Sandy soils tend to be droughty and low in nutrients. Clay soils often drain slowly.

Compost will benefit almost any soils, improving the water-holding capacity and nutrient retention of sandy soil and improving the drainage of clay soil.

"Composts are rich sources or nutrients," Dickerson said. "Although the quantities of nutrients in compost tend to be rather low, the nutrients are in organic forms that make them more stable, slowly releasing the nutrients over time for uptake by plant roots. Humic acid in compost also makes their nutrients in our alkaline soils more available for plant uptake."

Backyard composts can be applied fairly liberally to home vegetable gardens (1,000 pounds/1,000 square feet). Biosolid (sludge) composts and dairy manure composts should be applied at lower rates due to their higher nutrient contents that could burn new seedlings if not irrigated correctly.

Till compost into the soil to a depth of 6 to 8 inches for good distribution throughout the root zone.

"Unlike peat moss, compost is alive with all kinds of microorganisms," Dickerson said. Municipal composts made from shredded woody landscape wastes tend to behave like natural fungicides. "In experiments we've conducted in the field and in the greenhouse, a biosolid compost from the City of Albuquerque was found to suppress seedling diseases in chile and snapdragons."

Compost also can be used as mulch around vegetables and in flower beds. "It helps control weeds, reduces evaporation of water from the soil and acts like a slow-release fertilizer," Dickerson said.