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. 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 barnlot. 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.
How Mulches Save You Work and Benefit Your Soil
Any material applied to the surface of the soil as a barrier, to retain moisture in the soil, prevent weed growth, etc., is a mulch. Plastics, roofing paper or insulation fiber will serve. However, natural organic materials are the things most often used; they decompose in time, contributing to soil improvement.
A good mulch should let rain seep through, but be tight and thick enough to smother sprouting weeds. Usually it is applied four inches thick in shrub, vegetable or flower beds but it soon packs down to only a few inches. More can be added if bare spots develop or if weeds start coming through. New lawns require only a loose fraction of an inch of a fine-textured mulch to allow the grass plants to push their way through.
Organic mulches decay toward their bottom where they meet moist soil. This benefits the soil through the release of nutrients and materials that help make the soil surface crumbly and receptive to moisture. The mulch also helps by insulating the soil against extreme temperature changes and rapid drying.
One of the handiest sources of mulching material around the home is lawn clippings. Spread them no more than an inch thick at a time until they dry. Finished compost is excellent, if you have enough, but it is used better if worked into your soil. You can purchase any number of materials at the garden store, including peat, rice hulls, pulverized or ground bark, wood chips, etc.
In some localities tree trimming companies chip up trimmings which you can obtain free for the hauling. They make an acceptable mulch. Sawdust tends to pack a little tight, so rain and air cannot penetrate, but after it has partially decayed it is satisfactory. Hay, straw or similar local materials are useful where their appearance is not considered unsightly and if weed seeds are not being imported.
Sometimes much of a plant's root system grows just under the mulch, as for example the azalea's. Then one has to be careful not to disrupt the mulch by too much cultivation. In the vegetable and flower garden, the mulch functions during the annual growth period; after that, it can be tilled into the soil, or left on permanently and added to as needed.
Back to where you started
Back one page: How To Improve Your Soil
Next: Fertilizers and Plant Foods