What You Should Know about Organic Materials

The term organic material refers to living organisms or their remains, as opposed to inorganic or nonliving rock and its decomposed forms. Thus fallen leaves, twigs and stems, and corpses of animals are all organic. In speaking of the organic content of soils we assume that the material is at least partially decayed; the result of such decomposition is a black substance with a woodsy smell called humus.

Some gardeners practically worship organic matter, while others may not appreciate it enough. A little in the soil is almost essential for pleasant gardening; a lot is probably a luxury, more important to you than to the soil. But it is important to have organic matter in the soil. Organic crumbles in the soil are reservoirs for plant nutrients and water. The plant's root hairs surround these little batteries and, as the organics break down, absorb the released nutrients with the aid of bacteria, mycorrhiza and other soil creatures. This storage is what makes organic material essential to plant growth. And like all storage batteries, organic matter should be replaced as it is broken down and used up.

Organic matter loosens a tight soil by keeping the soil particles apart. Plants roots have to constantly add new root hairs at their ends to absorb nutrients; old roots are mostly used for plumbing and anchorage. Those root hairs have an easier time moving through an organic soil.

In nature, soils range from the nearly organic-less desert soils and coastal sands, to the nearly all-organic mucks of low lying areas. There is no set organic content that makes a garden soil good. The best prairie soils seldom have more than a few percent organic content, which is a clear indication that small quantities have great influence. It takes only a few percent of organic matter to make any soil friable and more responsive. By and large, inland soils contain less organic matter than coastal ones, because where temperatures are generally higher, all biological activity is speeded up, including decomposition.

Most of the humus in soils has accumulated through the ages from plants and animals that have died. However, Man adds organics when he spreads manure, compost, processed wastes, forest residues such as compost or shredded barks, and agricultural residues such as rice hulls and seed meals. All of these materials return to the soil essentially the same elements that were extracted from it to make the plants or animals that fed upon them. As an additional good point, organics also provide food for the many microorganisms in the soil that are on the whole beneficial to its structure and fertility.

With so many seeming advantages, it is easy to overestimate the importance of organic materials. The fact is, that with enough work, crops can be grown year after year on the same soil without the addition of organic material. Of course, ample fertilizer is used on a tightly regulated schedule. Some of the most expensive, productive land in the country--the Central Valley and other irrigated soils of our State and Arizona--yield excellent harvests though the soil is almost devoid of organic content! With enough fertilizer and constant soil management practices you can grow a lawn and garden on almost any soil. But you cannot necessarily make the soils easy and pleasant to dig into without plenty of organic material.