Oak trees need varying amounts of fertilizer based on their age and rate of growth. They perform best when fed a complete balanced granular fertilizer You can use quick-release or slow-release formula. Using a fertilizer formulation containing trace elements or micronutrients such as iron and zinc can benefit the tree and is a bonus when buying a fertilizer product for your trees.
Fertilize young oak trees from 3 to 5 years old twice a year with a complete and balanced formulation such as a 10-10-10 or 8-8-8. Apply according to the label directions and do not exceed 1 1/2 lbs. for every year of age. Make the first application in early spring and the second in early to midsummer.
Feed mature oak trees over 5 years old once per year or every other year in the spring at a rate recommended on the package label for the square footage under the tree canopy to at least a foot or two past the drip line.
Feed oak trees 3 years old or younger very lightly if at all to encourage root development over top foliage development. Apply the complete granular fertilizer at a rate less than half a pound for every year of age.
Apply any fertilizer over watered soil to eliminate the risk of burn and to speed percolation of the nutrients into the soil. Water in the fertilizer well a second time after applying.