Fruit trees are fertilized to ensure continued growth and fruit production.
In the backyard orchard, proper pruning in addition to the application of nitrogen in the spring prior to or at bud break helps maintain this productive status.
Other than nitrogen and zinc, iron and manganese may limit growth due to our alkaline soil conditions.
Apply nutrients based on a soil test analysis conducted by the soil testing lab at Colorado State University or another analytical lab of your choice.
The amount of nitrogen to apply can be based on how much shoot growth occurred the previous season or on a soil analysis.
Identifying Annual Growth
Each year of growth can be identified by the ring of bud scale scars remaining when the bud at the tip of the shoot grows.
A difference in color and/or bark texture is typically evident above and below the annual growth ring.
Check last year’s annual growth rate at several points around the tree to determine the average length of last year’s growth.
Use the average length of annual growth to determine if and how much nitrogen should be applied.
Applying Nitrogen Based on Annual Growth Rate
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 1 foot above ground level).
If too much nitrogen is applied it can lead to excessive leaf and tree growth over fruit production.
The maximum rate of nitrogen to apply to pome fruit trees (apples and pears) is 1/10th pound of nitrogen per inch of trunk diameter (measured 1 foot above ground level).
Apply this amount if growth the previous year was at the low end of the recommended rate.
As with stone fruits, apply less nitrogen the closer the actual growth rate approximates the recommended growth rate.
Maintain a record on the amount of nitrogen applied each year and the resulting growth.
Such records provide a guide for the amount of nitrogen fertilizer to apply to achieve the desired results.
Calculating the amount of fertilizer applications
Fertilizer products contain specific quantities of nutrient based on percentage by weight.
This is indicated on the product label, such as 15-1-1.
The first number (15) is the percentage by weight of nitrogen, the second number is the percentage by weight of phosphorus (P2O5) and the third is the percentage by weight of potassium (K2O).
For example, ammonium sulfate (21-0-0) contains 21 percent nitrogen while blood meal contains 12 percent to 13 percent nitrogen.
The amount of the fertilizer product needed is calculated by dividing the pounds of nutrient needed by the percent of that nutrient in the product.
If you need 1/2 pound of nitrogen for a given area and are using a product with 15 percent Nitrogen, divide .5 (one-half pound) by .15 (the percent of N in the product).
This tells you 3.33 pounds of this product are needed to apply 1/2 pound of nitrogen.
Pruning and excessive irrigation
Pruning the same amount each year will result in the same amount of stimulated growth.
If the tree is pruned more severely, apply less nitrogen fertilizer.
This will help avoid excessive growth.
Irrigating too frequently or too much at one time, as is common with fruit trees planted in turf areas, stimulates growth and subjects fruit trees to possible root rot diseases.
Take into account excessive irrigation and correct if possible.
Eliminating the grass around the base of a fruit tree and applying a thin layer of mulch is recommended.
Kill the grass with a glyphosate product, horticultural vinegar or fatty acid product such as Scythe before applying mulch.
It is highly recommended to plant the backyard fruit orchard away from turf where the trees can be watered and fertilized based on their needs and not that of turfgrass.
Placement of Fertilizer
Nitrogen and other nutrients, with the exception of zinc, can be broadcast over the ground and watered in, or applied in a band in the irrigation furrows prior to irrigation.
Do not apply fertilizer against the trunk as tissue damage may result.
Spread the fertilizer evenly and do not dump it in a pile at the base of the tree or injury will result.
If the area to be fertilized is more or less than 1,000 feet, calculate the amount of fertilizer to apply accordingly.
Foliar applications can also be used if appropriate materials are chosen. ❖