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Index : Citrus and Other Fruits
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- 17. It's Time to Fertilize Citrus - Top
With the approach of spring, citrus trees will soon come into full bloom. To promote this flowering and the subsequent development of fruit, it's important to fertilize citrus trees now.
Citrus trees need both nitrogen and phosphorous to grow properly. You can supply this by using a fertilizer such as ammonium phosphate (16-20-0), or you can use a similar analysis specially prepared citrus tree fertilizer.
Young trees (1 to 2 years after planting) will require about one-half pound of fertilizer.
Small trees (2 to 3 years after planting) will require about three-quarters pound.
Mid-sized small trees (3 to 4 years after planting) will require about a pound and one-half.
Small adult trees (4 to 5 years after planting) will require about two pounds of fertilizer.
Mid-sized adult trees (5 to 6 years after planting) will require about two and one-half pounds.
Large-sized adult trees (more than 6 years after planting) will require about three pounds of fertilizer.
Spread the fertilizer evenly under the tree, starting near the trunk and going out several feet beyond the branch ends. After spreading the fertilizer, lightly scratch it into the top quarter inch of soil using a garden rake. Next, water the fertilizer in slowly. I like to use a soaker hose for watering. If you have basin watering, simply fill the basin and allow the water to soak in.
Citrus trees generally need to be fertilized three times during the year; in February, May and August. Apply the same amount of fertilizer with each application. A caution however, do not over-fertilize! Citrus trees that get too much fertilizer will develop thick peels on fruit. If your citrus tree is growing vigorously and has dark green leaves, cut back on the recommended fertilizer amounts. You may want to skip one of the recommended all together if the tree appears healthy.
At this time of year, probably the most common concern over citrus trees is the yellowing and dropping of older leaves. Fortunately, this is a normal leaf drop that all evergreen trees experience during the winter months. As leaves age, they drop off. On citrus, this usually occurs just prior to new spring growth.
It is normal for new leaf growth on citrus to be yellowish-green in color. However, if over time these new leaves fail to turn dark green, there may be a need to add iron to the soil. Don't use just any iron product. I recommend chelated iron. It is more expensive than other forms but it is the only type that works in our alkaline desert soils. Two excellent chelated types of iron are Sequestrene 138, also sold as Ferrione 138.
Curling of new leaves and whitish colored streaking in the leaves is a sign of thrip feeding. Thrips are tiny cylindrical flee-like insects that feed by scraping the surface of the leaf. As a result leaves become distorted, but remain green for the most part. Thrips feed on virtually all citrus trees. However, the damage they cause is insignificant and no control is necessary.
Proper fertilization of citrus should help maintain the trees vigor and fruiting. If your citrus tree lacks vigor, has poor fruit production and branch die-back, check at the base of the trunk. The first set of roots should be at, or near, the soil surface. If you must dig down around the trunk more than one or two inches to find the first set of roots, the tree has been planted too deeply, or soil has washed in around the trunk. In any event, this soil should be removed. A barrier should then be placed around the trunk to keep the soil from washing back. Soil in contact with the trunk will cause a slow decline and eventual death of the tree.
Written by John Begeman, College of Agriculture and Life Sciences, the University of Arizona, 520-626-5161.
- Updated: February 16, 2003
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