Avocado, know botanically as Persea americana, are evergreen, fruit-bearing trees that are fertilized similarly to citrus trees, such as orange and lemon. You will often find fertilizer products designed and marketed for both citrus and avocado trees, in one. According to the University of Hawaii, young trees not yet of fruit-bearing age should be fertilized with a higher ratio of phosphorous than fruiting trees to ensure a vigorous root system.
Fertilize your avocado trees one to four times per year, beginning in the spring, in accordance with the product label dosing recommendations. You will need to apply slow-release fertilizers at less frequent intervals than fast-acting fertilizers.
Feed young avocados trees that are not yet producing fruit with a 10-30-10 fertilizer or similar, high-phosphorous formulation.
Feed your mature fruit-bearing trees with a 10-5-20, a high potassium quotient, to support fruit development.
Put on garden gloves and scatter the recommended dose of fertilizer evenly over the entire root zone, beginning 1 foot or so out from the trunk and spreading 1 to 2 feet beyond the outermost line of the canopy.
Water the fertilizer into the soil well and evenly, drenching the soil to a depth of at least 1 foot with each application. This will drive the nutrients down into the root zone.