As we begin our rainy summer season the following is a guide to help you with the symptoms of various nutritional deficiencies that you might notice. This can help you decide which, if any, fertilizer to use.
There are sixteen known elements required for healthy plants. Three of these, carbon (C), hydrogen (H) and oxygen (O) all can be obtained directly from air and water. The other thirteen elements are supplied through the soil. These are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), chlorine (Cl), copper (Cu), zinc (Zn), manganese (Mn), iron (Fe), boron (B), and molybdenum (Mo).
Each of these elements has a specific function in plant growth and development. If one or more of these nutrients are present in excessive amounts, toxicity or a nutrient imbalance can occur. Or if one or more of these essential elements are in short supply a deficiency can result. Either way plant growth and/or quality may be affected.
The nutrients, nitrogen, phosphorus and potassium are the main components, or macro-nutrients, of fertilizer. Sulfur, the remaining macro-nutrient, may not be a component of fertilizer and should not be overlooked. Look for fertilizer containing sulfur coated urea nitrogen.
The micro-nutrients to be used sparingly are boron, copper, iron, manganese, molybdenum, and zinc. Chlorine ordinarily is not valued as a plant food in fertilizer. It can be injurious if high percentages are present, but small amounts may be beneficial under some conditions. If you have plants or lawn around your pool equipment or overflow which don’t do well it may be chlorine toxicity.
Micro-nutrients are required by plants in low quantities so you should apply them cautiously. If a deficiency is suspected, it would be unwise to randomly apply all of the micro-nutrients. The result might be correction of one deficiency while inducing a toxicity of another micro-nutrient. Foliar analysis is the most accurate way to determine if a micro-nutrient deficiency needs correcting. The Collier County Extension Office can help you with this test. Individual micro-nutrients are available with suggested rates provided for application. However, it is essential that all micro-nutrients be provided in your fertilizer program at least once a year. Fertilizer formulations are available for shrubs, citrus, palms, etc. containing a good balance of these necessary micro-nutrients. Nutritional sprays are liquid formulations that contain the micro-nutrients. These sprays allow the elements to enter the plant through the leaf surfaces. The micro-nutrients can be tied up in our alkaline soil, due to improper pH, when applied as a granular fertilizer and may not be available to the plant. Therefore, when a micro-nutrient deficiency is apparent, it is more effective to apply a nutritional spray.
General symptoms of nutrient deficiencies are as follows:
Nitrogen – yellowing of entire plant with lower leaves worse and stunted.
Phosphorus – main veins of old leaves become purple or reddish. On fruit trees blossoms drop, fruit is small and matures slowly and few flower buds are formed for next year’s crop.
Potassium – light yellowing, then browning of leaf margins on old leaves. Then veins become yellow.
Manganese – mottled yellowing between midrib and primary veins. Entire leaf may turn yellow but midrib and large veins stay green longest. Frizzle top, yellowing, dwarfing and distortion.
Iron – pronounced yellowing on younger leaves, with veins appearing as a pale green or yellow to white if acute. Dwarf leaves, leaf fall, dead wood, dead tips and reduced growth.
Magnesium – yellowing begins on the margin and near the center of old leaf, progresses inward and downward; the tip, upper margin and lower central veins may remain green; necrosis and leaf drop.
Molybdenum – often mistaken for herbicide damage. Dwarfed leaves with irregular, wrinkled margins and prominent midribs and main veins on young leaves and shoots.
Boron – plants grow slowly. Terminal buds die and plant tends to be bushy. Later, lateral buds die, leaves thicken and fruits, tubers and roots become cracked and discolored.
Copper – usually confined to peat or muck soils. Slow growth or complete cessation of growth. Tips affected first and eventually die back.
Zinc – leaves become long and narrow, then turn yellow and become mottled with dead areas. Symptoms similar to iron deficiency.
To avoid the above problems your plants should get a good feeding in the spring months using a quality slow release fertilizer with minors. If you notice symptoms in your plants after many heavy summer rain storms give them a light feeding to get them through the rest of the summer until you do another complete fertilizing in the fall.
Fertilizer is fast becoming an issue as the waters of the Gulf of Mexico continue to decline in health. While fertilizer is not the only culprit, it is definitely one of the players. Lawns, trees and shrubs do not need as much fertilizer as some would have you think. Begin with twice a year for your shrubs and then just fertilize those that are showing signs of need. Palms and citrus are two exceptions needing three to four applications a year. Most native plants in your yard should breeze right through the seasons with almost no needs at all. When in doubt send a soil or tissue sample to determine the plant’s exact needs. You can find the information on how to do this at the University of Florida web site. If we all do our part, perhaps we can slow down the decline of the waters that surround us.