What Fertilizer to Use for Citrus?

Planting

• Plant your citrus tree during the early fall or winter, and fertilize once new buds start to develop. Feed every six weeks for the first year, using a balanced, granular fertilizer enriched with micro-nutrients such as magnesium, manganese, copper and boron. Aim to provide each tree with between 0.15 and 0.30 pounds of actual nitrogen.

Growing Trees

• In the second year, provide up to 0.60 pounds of nitrogen in five doses; in year three, up to 0.90 pounds in four doses; in year four, up to 1 pound in three doses; and in year five, up to 1.4 pounds in three doses. Spread the fertilizer underneath the canopy of the tree, but keep it at least a foot from the trunk as direct contact can damage the bark.

Mature Trees

• Fertilize citrus trees that are older than five years three times per year in January/February, April/May and September/October. Feed up to 1.5 pounds of actual nitrogen per year per large citrus tree. Mature grapefruit trees require half the amount of fertilizer as other citrus species, according to the University of Arizona's master gardener George Chott.

Types of Fertilizer

• Fertilizer for citrus trees comes as dry granules. Each sack or packet of fertilizer has a bold type number, such as 10-10-10, on the front that indicates the blend of nutrients. The first of these three figures indicates the percentage by weight of nitrogen. A 50-pound sack of 10-10-10 fertilizer contains 10 percent nitrogen or 5 pounds of nitrogen.