Fruit trees are fertilized to ensure continued growth and fruit production. The application of nitrogen in the spring prior to bud break helps maintain this productive status.

The amount of nitrogen to apply depends on the growth the previous season. Reduced fruiting wood and reduced fruit production results when the growth rate is less than what is recommended in the following tables.

Stone fruit trees (i.e. peach, cherry, plum and nectarines) can be fertilized at a maximum rate of 1/8 pound of nitrogen per inch of trunk diameter (measured one foot above ground level). This amount would be applied if the tree's growth was on the low end of the recommendation given in the tables. Less fertilizer should be applied if the previous season's growth rate falls in between the recommended growth increments.

Pome fruits (apples and pears) are fertilized at a maximum rate of 1/10th pound of nitrogen per inch of trunk diameter (measured one foot above ground level). This amount would be applied if growth the previous year was at the low end of the recommended rate. As with stone fruits, less nitrogen would be applied the closer the actual growth rate approximates the recommended growth rate.

A record should be kept regarding the amount of nitrogen applied each year and the resulting growth. Such records will provide a guide for the amount of nitrogen fertilizer to apply to achieve the desired results.

Pruning stimulates growth. Pruning the same amount each year will result in the same amount of stimulated growth. If the tree is pruned more severely, less nitrogen fertilizer should be applied. This will help avoid excessive growth.

Dr. Alvan Gaus, former Colorado State University Extension Fruit Specialist recommended the application of a zinc spray at bud break in the spring. This spray can be prepared by mixing one tablespoon of zinc sulfate in a gallon of water. The spray should be sprayed to thoroughly cover the tree. Apply the spray until the bark is no longer able hold the spray and the spray runs off the tree.

The application of other nutrients should be based on the results of a leaf analysis.

The actual amount of nitrogen differs between fertilizer products. For example, ammonium sulfate is 21 percent nitrogen while ammonium nitrate is 33 percent nitrogen. In other words, 5 pounds of ammonium sulfate (20% N) contain one pound of nitrogen. Three pounds of ammonium nitrate (33% N) contain one pound of nitrogen.

A five inch diameter peach tree may require up to 5/8 pound of actual nitrogen. To compute the amount of ammonium nitrate to apply, the following formula is used:

Nitrogen (N) can be broadcast over the ground and watered in, or applied in a band in the irrigation furrows prior to irrigation. Fertilizer should not be applied near the trunk as burning may result.

References:

Childers, N.F. 1978. Modern Fruit Science. Rutgers University.
Larsen, H.J., A.G. Gaus, R.J. Zimmerman, M. Rogoyski. 1998. Colorado Tree Fruits: Pest and Crop Management Guide. Colorado State University Extension bulletin XCM-41.
Westwood, M.N. 1978. Temperate-zone Pomology. W.H. Freeman and Company.