Humus, Composts, and Mulches

How You Can Produce Humus

An easy old-time method of increasing soil organic content was to grow ryegrass or soybeans, and then plow them under as a green manure. You can do this in between harvests if you grow a winter cover crop such as Crimson Clover. Much the same effect can be obtained by mixing purchased organic materials--such as peat--into the soil. But avoid introducing weed seeds. This will be a hazard if you obtain manure from a local barn lot. There may be weed seeds in the hay, or even in piles of sawdust left to rot at the mills.

Such organics yield humus when they decompose, but they should be mostly decomposed when you use them. If organic materials high in carbohydrate (such as sawdust or straw) are mixed fresh into soil, a temporary imbalance of fertility results until decay has progressed. The little organisms which cause rotting compete with garden plants for nitrogen. If you are mixing incompletely decomposed organics into your soil, you should add at least a pound of actual nitrogen to each 1,000 square feet or your plants may starve at the very time you think you are helping to nourish them.

Often organics are first put on as a mulch--that is, a surface layer. Some decomposition occurs during the growing season, and then the residues are mixed into the soil.


Many gardeners prefer to have a compost pile where they dump weeds, fallen autumn leaves, and grass clippings, and allow them to decompose into humus. Practically anything that was once alive can be added, including garbage from the kitchen such as non-meat table scraps, egg cartons, paper towels, eggshells, coffee grounds, shredded paper from the office, etc. Various techniques are used, but the main objective is to encourage the microorganisms to attack the organics. These little organisms need moisture and air in order to flourish. So a compost heap should be arranged to drain adequately, but it should be dished out at the top to trap water rather than shed it. In some instances, purchased bacteria or earthworms are added, but usually nature supplies these adequately.

For quick composting, layers of rich soil are often interspersed between the organic material, possibly with lime and fertilizer added as well. Loosening or turning the compost aerates it and speeds the decomposition. A well-laid pile will function even in winter, for the internal activity releases heat.

The time it takes to produce humus, in favorable conditions, may be only a few weeks. But if you are not in a hurry, you can pile things up as they accumulate, and they will gradually rot to black humus in the oldest part of the pile.