Organic matter is the food of soil organisms. In nature, most of the organic matter in the soil comes from dead plant parts and animals that drop to the ground and decay. A complex world of bacteria, fungi, worms, and insects cycle and recycle the nutrients in the organic matter until all the energy is wrung from it, leaving a brown, sticky material called humus.
Organic matter helps all soil, and is the salvation of some. For example, soils at the extremes of the soil texture spectrum—very clayey or very sandy—are both improved by organic matter. Heavy clay is made more permeable to air and water, and easier to work. The capacity of sandy soil to hold water and nutrients is increased by the absorbency of the organic matter.
For the quickest action, till the organic matter into the top 6 inches of soil, where most of the plant roots are. If this isn’t possible, just spread it on the surface. Earthworms, ants, and other insects will pull it into the soil for you.
Wise gardeners add organic matter in any way they can, and as often as possible. Here are some of the methods that help:
- Dig in organic matter whenever you till a bed. When turning over a vegetable garden or annual bed, dig in a few inches of organic matter.
- Add organic matter to the backfill soil when you plant flowers, shrubs, and trees.
- Mulch with materials that decompose. Although rocks, gravel, and firbark chunks make excellent mulches, they don’t decompose and add organic matter to the soil. Mulch with leaf mold or other finely-ground organic materials. They will decompose where the mulch is in contact with the soil, adding their humus to it. When the mulch wears thin, just add more.
- Add compost. Compost is partially-decomposed organic matter. As such, it is in a more concentrated form than “raw” organic matter, and easier for the soil to digest. The compost can be incorporated into the soil, or sprinkled on top.
- Sift organic matter into lawns and ground covers. Sprinkle compost or other fine-textured organic matter on lawns or low ground covers and work it into the plants with the back of a rake. You can work from 1/2 to 1 inch of compost into a lawn without covering the grass.
- Sweep leaves under plants. Whenever possible, tuck raked-up leaves and pulled weeds under the foliage of shrubs, ground covers, or any other place where their appearance won’t be offensive.
- Select organic fertilizers. Although more expensive and bulkier to handle than chemical fertilizers, organic fertilizers have the advantage of adding organic material at the same time as they add nutrients.
- Till in green manure. For centuries, farmers have raised “green manure,” a crop of grass or other fast-growing plants that are grown to a height of a foot or so, then tilled into the soil. Annual ryegrass is frequently used, or select any plant that grows rapidly in your climate.