Whenever a plant appears to be dying, a great many homeowners inquire about having soil tested in the mistaken belief that the decline of the plant resulted from a lack of nutrients in the soil. After growing well for a long period of time, however, a plant will not suddenly wilt and die due to malnutrition. It would be very rare to find a garden soil so low in nutrients that it would not support plant life. In fact, more plants are killed from over-fertilization than from not enough. A number of factors can cause plant failures which are not revealed by soil testing.
Poor drainage, particularly during wet weather, is one of the major causes of plant failure. Wet soils contain little oxygen, which is needed in greater amounts than other elements for healthy plant growth. When a plant's root system is deprived of oxygen, it can no longer perform its function of absorbing water and nutrients from the soil. Left uncorrected, such waterlogged soil will ultimately kill the root system and subsequently the entire plant will die. Conversely, during periods of drought, plants need additional water for survival.
Soil tests also do not indicate the presence of insects or disease organisms. Plants should be carefully examined for signs of insect damage, indicated by holes in the leaves caused by chewing insects or by yellowing of leaves from sucking type insects. Brown spots on leaves and branches would be an indication of a fungus problem, which can be controlled by the application of copper fungicide.
The indiscriminate use of herbicides or weed killers will often result in the sudden death of plants. Unfortunately, soil testing does not reveal this information either.
Infestation of plants by microscopic worm-like animals, called nematodes, would not be revealed by ordinary soil testing. Nematodes damage plants by feeding on the root systems. Affected roots appear shriveled, blackened and stubby, and there generally will be an absence of white feeder roots.
The next time you have a soil problem which you think might be related to lack of fertilizer, please examine your growing conditions (water, drainage, insects, disease and nematodes) to determine whether any of the above mentioned factors are causing the problem. If none of these are relevant, then you may consider having your soil tested.
Soil tests performed at your County Extension office indicate the pH (acidity or alkalinity) of the soil. Generally, south Florida soils are alkaline, and it is necessary that an acidifying agent be added to the soil. Such acidifying agents are sulfur, iron sulfate, aluminium sulfate and organic material.
DATE: July 1986
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