The Q&A Archives: When to fertilize grapefruit

Question: When do I fertilize my grapefruit tree and how much and what kind to use.

Answer: Citrus should be fertilized with a nitrogen fertilizer product 3 times per year in Jan/Feb; Apr/May; and Aug-Sept. Each feeding should contain 1/3 of the tree?s total annual nitrogen requirements. Requirements vary according to the age and size of the tree. According to the University of Arizona Cooperative Extension, a newly planted citrus tree takes 0.12 pounds of actual nitrogen per year, so each feeding would be 1/3 of that. A tree 1-2 years in the ground, takes 0.25 pounds of actual nitrogen. Keep adding 0.25 pounds every year or so, until the tree is 6 or more years old. At that point, the mature tree takes 1.5 pounds of actual nitrogen annually. However, grapefruit trees have a twist: After 5 or more years, they take half of these amounts. The amount to apply depends on the percentage of nitrogen in the product. If you don't want to figure that out, you can buy a fertilizer formulated for citrus, but it's more expensive than just plain nitrogen (such as ammonium sulfate). Spread fertilizer at the outer edges of the tree canopy, or dripline, where feeder roots can absorb it. Water deeply immediately after applying fertilizer. For a handy chart with fertilizer requirements, see "Desert Landscaping for Beginners," 0-9651987-3-1, Arizona Master Gardener Press. Good luck with your tree!

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