Percentage of Organic Matter in Soil

Adding compost to your garden increases organic matter levels.

Organic matter consists of dead plant and animal material that is undergoing breakdown by soil microbes. The addition of organic matter improves drainage for some soils while for others it increases aeration. It also helps soil retain nutrients.

The Right Amount

The ideal soil should contain between 5.0 percent and 6.0 percent organic matter. A routine soil test can determine the amount of organic matter present in your soil.

Adding Organic Matter

Increasing the amount of organic matter in your soil requires incorporating plant or animal material into the soil. Commonly used sources of organic matter include compost, well-rotted manure, peat moss and dead leaves. Since organic matter decomposes over time, you must replenish it each year. Organic matter breaks down faster in hot, humid climates and in well-aerated soils with a pH between 6.0 and 7.0.

Too Much of a Good Thing

While too little organic matter can cause drainage and soil compaction problems, too much can overstimulate soil microbes, causing them to compete with plants for nutrients.

References

• University of Massachusetts Extension: Soil Basics -- Organic Matter
• "Rodale's Ultimate Encyclopedia of Organic Gardening"; Fern Marshall Bradley, Barbara W. Ellis and Ellen Phillips, editors; 2009