Institute of Food and Agricultural Sciences
Hendry County Horticulture News
Citrus Fertilization for Home Owners
Fertilization is an important part of a program of care for the bearing citrus tree. Inadequate nutrition is one of the most serious problems faced by home owners growing citrus on our poor sandy soils. Three applications of fertilizer for mature bearing trees on well drained sites is sufficient. The best time to apply fertilizer is before or during the flush of new growth that is produced periodically throughout the year occurs. Fertilizer is typically applied in January or February, May or June, and November or October.
Citrus fertilizers are formulated to provide adequate amounts of the basic fertilizer elements: nitrogen, phosphorus and potassium, as well as the minor elements: iron, boron, magnesium, manganese, zinc and copper. For average soil conditions, the following fertilizer analysis (1%N-1%P-1%K-0.20%Mg-.05%Mn-0.025%Cu-0.0033%B) or equivalent citrus fertilizer (6%N-6%P-6%K-1.2%Mg-.3%Mn-.15%Cu-.02%B) will generally be satisfactory for door yard citrus trees. Such mixtures are commonly marketed as "Citrus Special" fertilizers. This mixture can be used for all three applications throughout the year.
The amount of fertilizer applied is important. Over fertilization tends to make the tree excessively vegetative, with a resulting reduction in the quality and quantity of the fruit. In addition, over fertilization is wasteful and can lead to contamination of ground water supplies. To maintain foliage of a good dark green color, a fairly safe rate of application is one pound of 6-6-6 citrus fertilizer per year of age of the tree. A total application of 20 pounds per year divided into 3 applications will be sufficient for trees 8 years old or older. Fertilizer should be scattered evenly over the root zone in an area twice the diameter of the tree canopy.
The pH (acidity or alkalinity) of the soil is an important factor in the nutritional program. The ideal range is between 6.0-7.0. At this range the macronutrients, such as nitrogen, phosphorus, potassium, calcium, magnesium and sulfur are most available to the plant. At higher pH levels, above 7.0, many minerals may become unavailable to the plant. This is usually evidenced by the development of minor nutrient deficiency symptoms. On alkaline soils, a foliar nutrient spray may be used to provide needed minerals. These sprays can be used throughout the year except at flowering. Nutrient sprays are applied to the foliage and nutrients are readily taken up by the leaves.
Yellowing or lightness of color (other than on immature growth) is a sign of hunger in citrus. Specific nutrient deficiency symptoms include:
Nitrogen: Even yellowing of the entire leaf, appearing in older leaves first, premature leaf drop. Small fruit, thin peel.
Phosphorus: Small leaves, often displaying a purplish hue on green growth. Misshapen fruit. Coarse peel, dryish pulpy fruit.
Potassium: Yellow leaves with brown margins, heavy leaf drop at flowering. Small fruit, fruit drop.
Magnesium: Leaves with prominent green veins and yellow interveinal areas, green triangular area at the leaf base. Defoliation.
Manganese: Light green mottles between green veins, appearing first on young leaves. Leaf size and shape are normal.
Iron: New leaves become light green to whitish with dark green veins, older leaves may not show symptoms.
Boron: Fruit display gray and brown discoloration's with pockets of brown in the white of the rind.
Copper: Leaves are dark green, new shoots appear vigorous then become bowed in an s-shape. Leaves are large, twigs die back.
Zinc: Sparse yellow foliage with green veins. New foliage is small and distorted. Small fruit and leaves
Careful observation of your citrus trees and attention to nutrient deficiency symptoms combined with a good fertilizer program will pay off in fruit quality and quantity. Good luck and good gardening.
Gene McAvoy is the horticulture agent with the Hendry County Extension Service. Direct your horticulture questions to PO Box 68, LaBelle, FL 33975, e-mail - firstname.lastname@example.org or phone 863-674-4092 or 863-983-1598. You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle. Office hours are from 8:00 - 5:00.
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