Easy-to-use organic fertilizers have special benefits

By Lee Reich
The Associated Press

With all the concern about chemicals in our environment, some gardeners fear that using chemical fertilizers will poison people, plants or the soil. This is not the case — when chemical fertilizers are used correctly. But chemical fertilizers are too easy to use incorrectly. And this is where “organic fertilizers” come into play.

Organic fertilizers are natural materials that are unprocessed or only slightly processed. Manures, ground up rocks, and composted vegetable wastes are examples of organic fertilizers. Chemical fertilizers are synthesized and generally more concentrated sources of nutrients.

Even though nutrients “eaten” by a plant ultimately are the same whether the source is a chemical or an organic fertilizer, the nutritional effect is different. Most organic fertilizers must be decomposed by soil microorganisms before they can release their goodness to plants. Warmth and moisture stimulate the microorganisms as well as plants, so nutrients are released in synch with plant growth. Slower release means that one application can last a whole season and that there’s less chance of nutrients washing out of the soil before plants get to them.

Organic fertilizers vary in their concentrations of nutrients. Horse manure and compost have less than 1 percent nitrogen; soybean meal has 7 percent nitrogen; and blood meal has a whopping 15 percent nitrogen. But concentrated is not always better.

Much of the benefit of organic fertilizers comes from their bulk, which comes mostly from carbon compounds. These compounds help plants take up what nutrients are in the soil, as well as help release new nutrients from rock minerals. These compounds also include antibiotics that kill some fungi and bacteria that cause plant diseases. And the sheer bulk of these carbon compounds fluffs up soils, making room for air and, at the same time, sponging up water to hold for plants.

To treat your soil well, add to it abundant amounts of leaves, manure, straw, grass clippings and compost. Supplement these bulky materials, when necessary, with doses of more concentrated fertilizers. Supplementation is necessary for bulky materials such as sawdust and straw, which are very low in nutrients, and for plants such as celery and cabbage, which have voracious appetites.