Q: Last week’s question explained what compost is, but didn’t mention how to use it. Can you educate me on the best uses for compost?

A: Researchers are working hard to determine the best uses for compost. Currently, compost is applied at homes, farms, ranches, municipal and commercial landscapes for:

• soil incorporation to increase organic matter, fertility and water holding capacity
• top dressing on turf, gardens, trees and shrubs
• erosion control
• animal stall bedding
• alternative daily covers at landfills
• commercial potting soil mixes
• manufacturing of compost teas and extracts
• bio-filters to “scrub” air of odors and particulates

For home users, there are generally three ways to use compost: top-dressing, soil incorporation and mulching. Top-dressing compost is spreading a thin, ¼- inch layer of fine textured compost, usually on top of turf, and often after core aeration. Soil incorporation of compost is digging or tilling at least one inch of compost, six to eight inches deep. To mulch using compost, apply to the soil surface where plants grow, four to five inches thick for weed suppression, soil insulation and moisture retention. Never allow compost to come in contact with the base of plants.

Low salt content (0-15 mmhos/cm) in the compost is better for general home and garden use. The rates for compost use vary based on specific characteristics and types of composts, as well as intended use.

To determine your garden compost needs, the first step is to get a comprehensive soil test. For more information on soil testing, see Fact Sheet #0.500 - Soil Sampling and #0.520 - Selecting an Analytical Laboratory.

While you are waiting for recommendations, start compost shopping. Reputable compost producers generally have a printed analysis on their packaging, or separate documentation about bulk compost. This information will help you when your lab results and recommendations return. In addition, the Rocky Mountain Organics Council (RMOC) communicates and educates consumers about compost products. The RMOC is made up of compost manufacturers, CSU researchers, state regulators and stakeholders. Visit www.cafr.org.

The RMOC created a class system for compost, described below. In general, it’s best to follow specific guidelines for healthy soils.

• Class I = Mature, stable compost, low salts, 6.0-8.2 pH; can be applied at high rates for all growing needs.
• Class II = Mature, stable compost, medium salts, 6.0-8.4 pH; acceptable for all uses, including horticultural, nursery and container mixes. This compost should be incorporated 60 days prior to planting.
• Class III = Semi-composted, high salts <30 mmhos/cm, pH 6.0-9.0; compost should only be used for crop production, turf and top soil blends with limitations, as well as for backfill, erosion control, mulch and bio-filters. Deep incorporation and thorough mixing recommended. Note: Classes I-III will be tested and passed for pathogens and chemical contaminants
• Class IV = Non-composted materials; for agricultural use only.

Gardening and Insect Fact Sheets are available on-line by clicking HERE.

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This page updated:  April 13, 2007