Spring is here and it is time to fertilize before the dry, harsh weather of April and May arrive. Here are some facts to help you decide what to use.
There are 16 known elements required for plant growth and development. Three of these, carbon(C), hydrogen (H), and oxygen (O), are obtained directly from air and water. The other 13 elements are supplied by 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).
These 13 elements plants obtain from the soil must be in a slightly soluble form so they can be taken up by the plant’s roots. 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 a toxicity or 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 macronutrients, of a suitable fertilizer. Sometimes dolomite, a liming material providing both calcium and magnesium, may be included in growing media. Sulfur, the remaining macronutrient, may not be a component of the fertilizer and should not be overlooked. Look for fertilizer containing sulfur coated urea nitrogen.
The micronutrients 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 around your pool equipment or overflow which don’t do well it may be chlorine toxicity.
Micronutrients 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 micronutrients. The result might be correction of one deficiency while inducing a toxicity of another micronutrient. The most accurate way to determine a micronutrient deficiency in need of correction is to use foliar analysis.
The Collier County Extension Office can help you with this test. Individual micronutrients are available with suggested rates provided for application. However, it is essential that all micronutrients 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 micronutrients. Nutritional sprays are liquid formulations that contain the micronutrients. These sprays allow the elements to enter the plant through the leaf surfaces. The micronutrients 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 micronutrient deficiency is apparent, it is more effective to apply a nutritional spray.
Following are some general symptoms of nutrient deficiencies:
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: Faint yellowing, then browning of margins on old leaves. Then veins become yellow.
Manganese: Mottled chlorosis 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 fine green lines, yellow to white if acute. Dwarf leaves, leaf fall, dead wood, dead tips and reduced growth.
Magnesium: Yellowing begins on margin and near center of old leaf, progresses inward and downward; 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 your 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, turn yellow and become mottled with dead areas. Symptoms similar to iron deficiency.
When purchasing your fertilizer it is important to understand the fertilizer label on the bag. A 16-4-8 analysis on a 100 lb. Bag means it contains 16 lbs. Of nitrogen, 4 lbs. Of available phosphoric acid, and 8 lbs. Of soluble potash. The first number is always nitrogen, the second phosphorus, and the third potassium. In addition to these three primary nutrients any secondary nutrients, or micronutrients, are reported at the bottom of the label in a similar manner if they are guaranteed present.
For lawns a 16-0-8 or a 15-0-15 analysis are good choices. Turf needs more nitrogen than do woody plants for turf density. This allows it to fight off weed invasions, tolerate foot traffic, and resist attacks from insects and diseases. However, problems can result from over-application of nitrogen, notably disease. When the plant takes up too much nitrogen, its cell walls become thin, which makes it easier for a fungi to invade. This will cause a higher than normal water need. Also this lush growth attracts insects.
Nitrogen is available in two basic forms - inorganic and organic. Plants have a preference for the inorganic, or nitrate form of nitrogen. There are two primary organic forms of nitrogen. One is a manmade organic called urea. The others are all the naturally occurring organic materials such as sewage sludge and manures. These organic forms of nitrogen are converted to the plant preferred nitrate form by bacterial action in the soil.
The soluble nitrate form of nitrogen is quickly available to the plant causing the rapid growth rate which may cause thin cell walls to develop. Nitrate nitrogen doesn’t last long in the environment. It can leach rapidly from the soil and may even be lost as a gas. Nutrients should be supplied at the same rate the plant can use them. This means soluble nitrates must be applied frequently in very small amounts.
Turf will have a higher quality using a slowly soluble or “controlled release” material. Look for the following when purchasing your lawn fertilizer.
- Sulfur coated urea. Nitrogen release occurs as water moves through tiny cracks and pinholes in the sulfur coating.
- Polymer coated urea. Urea granules with a polymer coating. Water diffuses through the coating to dissolve urea. Nitrogen release is affected by temperature and is more rapid in summer.
- Sulfur and polymer coated urea. Polymer coating is added to the sulfur coated urea as protection and to slow the movement of water into the core. It combines the cost advantage of sulfur coated urea and improved release of polymer coated urea.
While these fertilizers are more expensive your lawn will be healthier if you use them and thus cheaper to maintain throughout the year in terms of water, insecticides and fungicides.
Palms under three feet use 6-6-6 monthly for maximum growth. For palms over three feet four times a year in early spring, late spring, summer and early fall using a palm fertilizer at the rate of 1 lb. per foot of trunk. Be sure to use the micronutrients, especially manganese and magnesium, on your palms.
For shrubs, vines and hedges a good quality 6-2-6 or 8-2-8 analysis is recommended at a rate of 1 ½ lbs. per 100 sq. ft. Palm fertilizer is an excellent choice for all your acid loving plants. Four applications, in early spring, late spring, summer and early fall is optimal but I have found that two fertilizations using a quality slow release nitrogen with micronutrients, in early spring and early fall keeps the plants healthy and growing vigorously.
Bougainvillea prefers only once a year fertilization with 6-2-6 or 8-2-8 at a rate of 1/4 lb. per foot of height of bushy plant.
Citrus should be fertilized at a rate of ½ lb. Of 6-2-6 every six weeks for the first three years. Wait until new growth begins, after planting, before fertilizing. After three years apply 1 lb. per year of age of tree with each application of citrus fertilizer in January, June and October. Reduce to ½ lb. per year of age after ten years old. Also, if you missed the January fertilization wait until your fruit has set to fertilize. If your citrus are in bloom it may cause the blooms to drop resulting in a reduced crop.
I hope these facts make this necessary chore in your yard a little easier to understand.
Eileen and Peter Ward have owned a landscape and lawn maintenance company for 35 years. Eileen can be reached at Gswdmarco@comcast.net or 239-394-1413.