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Soil Organic Amendments

By Carl Wilson, Horticulturist with Denver Cooperative Extension

Soil improvement is a continual process. It often takes ten or more years to build a productive garden soil. If your soil is too sandy or too high in clay, the solution to both soil extremes is the same - add organic amendments such as compost, peat or manure.

Organic amendments break apart tight clays and hold water and nutrients in loose sands. Add a two inch layer over the surface of the soil - the equivalent of four cubic yards per thousand square feet. Mix in thoroughly to a depth of six inches by tilling or spading. With annual plants like vegetables and annual flowers, you have the opportunity to add amendments every year. With perennial plants like trees, you have a one time chance at planting.

The best organic amendments are coarse in texture. Fibrous sphagnum peats are useful but more expensive than compost or manure. Avoid using dusty fine sedge peats that clog soil drainage. Native Colorado mountain peats are generally inferior for soil amendment purposes and their harvest damages the environment by destroying stream hydrological systems. The best peats come from the northern U.S. and Canada.

Manures should be aged for at least one year. Fresh manure is to high in ammonia which burns plant roots. Avoid feedlot manures which are typically high in salts. Dairy cattle manure is generally a better quality product for plant growing purposes. Rabbit and poultry manures are fine. Watch weed seed problems from horse or sheep manures.

Compost is perhaps the best organic amendment. While you can purchase compost, home composting recycles yard prunings and clippings and keeps them out of the landfill. Compost promotes microbiological activity in soils so necessary for healthy plant growth. Consider composting to meet your soil improvement needs if you don't already.

For more information on soil improvement and how to compost at home, contact your local nursery or garden center, Cooperative Extension office, or botanic gardens.

Photograph courtesy of Judy Sedbrook.

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Date last revised: 01/05/2010