While having a soil test done is the best way to choose the right fertilizer for pecan trees, you can apply 5-10-15, 10-10-10 or 17-17-17 fertilizers annually, depending on location and age of the tree. In addition, you should use lime, zinc sulfate and ammonium nitrate.
According to Pecan Trees for the Home or Backyard Orchard, young trees (including those newly planted) need both fertilizer and lime. If the tree is a new planting, don’t put fertilizer in the hole as it may burn and kill the roots. During the June following planting, spread 1 pound of 5-10-15 fertilizer in a 25-foot-square area around the tree. Fertilize with 10-10-10 no closer that a foot from the trunk in March and June of the following year. If the tree doesn’t grow 2 to 4 feet in the following year, again in June or July, fertilize with 1 pound of ammonium nitrate per inch of trunk diameter and 1 pound of zinc sulfate per tree.
For trees that are already producing nuts, fertilize in March with at least 10-10-10 fertilizer, up to 25 pounds each for large trees and ammonium nitrate, up to 8 pounds per tree. To promote healthy leaf growth, fertilize with 3 to 5 pounds of zinc sulfate per tree, also annually in July or August. Also, since soil pH affects how well trees absorb nutrients, based on tree growth and health, you may have to fertilize with lime.