Fertilize yearly with an equal amount of nitrogen, phosphorus and potassium; a standard 10-10-10 fertilizer contains all of these nutrients. Slow releasing standard fertilizer tabs are more beneficial for citrus as they keep the nitrogen from washing below the root line.
Supplement annually with turf fertilizer as it contains magnesium, boron, copper and zinc. These nutrients should be applied and watered in annually. If you want to use a single chemical fertilizer, high-end citrus fertilizers combine the nutrients of standard and turf fertilizers into their slow release tabs.
Add mycorrhizal fungi into the soil. Mycorrhizal fungi is a natural plant root aid that attaches to the root system and enables plants to gain more nutrients from the soil. Mycorrhizal fungi is absent from most urban soils.
If the local soil is lacking in iron, supplement annually with iron tablets. If the tree's soil is above a pH of 7, then iron should be added.
Incorporate mycorrhizal fungi into the soil annually starting two seasons before planting the citrus tree.
Add fish emulsion fertilizer into the soil biannually beginning one season before planting the tree. After the tree has been planted, fertilize initially in the spring as the tree is budding, and again once its fruit has been harvested. Organic fertilizers will not burn the root systems of trees, so they can be safely applied on saplings as well as on mature trees.
Combine 5 cups of hot water with 1 lb. of coffee grounds and let sit overnight. Pour onto the tree's root system yearly at the start of spring for added soil acidity. For best results, apply at night and water in well.