Organic Gardening Think Mulch

by Wesley P. Judkins.

Wesley P. Judkins is Emeritus Professor of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg.

Organic gardening is the production of crops without the use of inorganic chemical fertilizers or pesticides. This means that only organic fertilizers such as manure, sewage sludge, cottonseed meal, bone meal, or dried blood are used. Also, diseases, insects, and weeds are controlled by natural resistance, birds, predator insects, or mechanical means, rather than by using pesticides or herbicides.

Organic methods may be followed with success in the home vegetable garden. This is especially true if mulches are used during the summer, and the crop refuse is returned to the soil each year to replenish and increase the organic matter content.

Regardless of the original source, fertilizer in the soil must break down into its ionic form before it can be used by plants. The ions which are then absorbed are identical, whether derived from an organic or inorganic source. Therefore, in terms of benefits to plants, when similar quantities of nutrients are available there is no advantage for either organic or inorganic fertilizer.

Organic materials are less caustic than inorganic fertilizers and, except for poultry manure, may be used with little possibility of damage to plants. The nutrients from organic fertilizers are rather slowly made available to plants. This may be an advantage where delayed release is desired to promote plant growth over an extended period.

Manure is commonly salvaged as a low cost fertilizer by farmers who produce livestock or poultry. It is usually not readily available to home gardeners. Dried manure with an analysis of about 1-1-1 may be used.

Other materials such as cottonseed meal, bone meal, and dried blood are available as organic fertilizers. These, and dried manure, are much more expensive than inorganic fertilizers. Also, from a practical conservation point of view, cottonseed meal, bone meal, and dried blood should be recycled as feed for livestock or poultry, and their manure then salvaged as fertilizer.

Most inorganic chemical fertilizers are much cheaper than organic types per pound of nutrient element. These elements become available for plants quite rapidly when applied in the inorganic form. Because of their concentration and solubility, inorganic commercial fertilizers are somewhat caustic and must be used with care to avoid damage to roots or foliage.

Sewage Sludge

Sewage sludge may serve as a desirable source of nutrients for gardens if a properly processed product is used correctly.

Raw sewage sludge, which is sometimes called primary or settled sludge, is a solid, lumpy material with an offensive odor. It is not recommended for use in the production of any type of crop, because it is a potential carrier of harmful pathogenic organisms.

Digested sludge is settled sludge which has been anaerobically decomposed. During this process, much of the organic matter is converted to gases and soluble material, and most of the pathogenic organisms are destroyed. The nutrient content of digested sludge is low and variable with an average of about 2% nitrogen, 2% phosphoric acid, and .5% potash. This type of sludge may be used on the home garden if applied in fall before the soil is prepared for planting the next spring.

Checking soil moisture under organic mulch of lawn clippings.

Dried activated sludge is settled sludge which has been treated with large amounts of air to cause aerobic decomposition. The resulting product is then heat dried and ground. The aeration and heat treatments inactivate any harmful pathogenic organisms. Activated sludge has a composition of about 6% nitrogen, 4% phosphoric acid, and .5% potash. This product may be used for gardens.