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Organic Soil Amendments

By Steve Cramer, Colorado State University Cooperative Extension

Good soil is a pre-requisite for good Gardening. Don't, however, expect soil improvement to occur "overnight." It can take 10 years or longer to build productive Garden soil. If a soil contains too much sand or too much clay, the solution to both is the same -- add organic material.

Organic materials, also known as organic amendments, break apart tight clays and hold water and nutrients in loose sands. Organic materials include compost, peat moss and manures.

To amend soil, add a two-inch layer of organic material over the soil surface. Use four cubic yards of organic material per 1,000 square feet of Garden area. Rototill or spade the material in thoroughly to a depth of 4 to 6 inches. When growing vegetables and annual flowers, you have the opportunity to add amendments every year. With perennial plants, such as trees and shrubs, you have only one chance to amend the soil and that is at planting time.

The best organic amendments are coarse materials. Fibrous sphagnum peats are good, but more expensive than compost or manure. Don't use dusty, fine peats that clog soil drainage. Native Colorado mountain peat generally is inferior as a soil amendment; in addition, its harvest destroys mountain wetlands and stream systems. The best peats come from the northern states and Canada.

Manures should be aged for at least one year and composted if being used on fruit and vegetable Crops. Fresh manure is too high in ammonia and burns plant roots. Avoid feedlot manures, which typically are high in salts. Dairy cattle manure generally is a better quality, but you also can use poultry manures. Some manures can carry weed seeds, spreading their growth.

Compost may be the best organic amendment. It can be purchased or made at home by recycling yard prunings and clippings. Compost promotes microbiological activity in soils necessary for plant growth.

Photograph by Judy Sedbrook.

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Date last revised: 01/05/2010