Originally Published In The Deseret News -- Wednesday, February 21, 1990
If you've been dreaming of luscious, tree-ripened peaches as you sit in your armchair this winter, you're going to have to do more than just dream! Fruit trees need proper care if you want to produce high-quality fruit.
One of the important aspects of caring for fruit trees is adequate fertilization. Fertilizers that may need to be supplied to fruit trees in Utah are nitrogen, phosphorus and micronutrients, including zinc, iron and manganese. Phosphorus may be needed if all topsoil has been removed. Potassium is seldom needed because of the abundant supply occurring in the soil and the water.
Fruit trees have a perennial root system that is able to extract minerals from a wide soil profile. This reduces the amounts and kinds of fertilizers we must apply. Nitrogen needs to be applied each year, as it is very soluble and leaches freely. It must be supplied to produce the highest-quality fruit. Determine the amount of fertilizer to apply by looking at the tree. Measure the length of the previous year's shoots on several branches and determine the average length.
The accompanying table gives the average length of shoot growth for healthy trees.
Increase the amount of fertilizer if the average length of shoot growth is below average and decrease the rate if the growth is above average. Shoot growth should not be thin or weak. Fertilizer is not a substitute for good cultural practices. It is not a cure for sick trees, particularly those that have root systems damaged by borers, root rot or other causes.
After you have determined the average shoot growth in inches, use the accompanying nitrogen table to give the amount of nitrogen needed for your trees.
Nitrogen is the first of the three numbers listed on the bags of fertilizer.
Fertilizer recommendations are generally given in pounds of actual nitrogen. The amounts given for ammonium nitrate and ammonium sulfate are larger because they have only 34 percent nitrogen and 21 percent nitrogen, respectively. This means if you are going to put on 1 pound of actual nitrogen for a tree that is 8 years old with average shoot growth, apply 5 pounds of ammonium sulfate.
Apply the fertilizer to the soil in a band below the outer edges of the branches. This area is commonly referred to as the drip line of the tree. If your trees are younger, the width of the fertilizer band should be about 2 feet wide near the trunk. If you have mature trees, make the band 2-3 feet wide and at least 8-10 feet away from the trunk.
Fertilizer should be spread on the soil or snow sometime before early March. Researchers have discovered that the roots of trees start growing at least six weeks prior to the time the tops start growing. Fertilizing now will ensure that adequate nutrients are available as the plants begin their growth cycle.
Fertilizing fruit trees should be carefully coordinated with your pruning program. Dwarf trees should not be allowed to bear fruit too young. This will stunt the tree, and fertilization will not correct the problem. On older trees or poorly trained trees that require a heavy pruning, apply less fertilizer in years they are pruned extensively.
Trees that set large amounts of fruit will need more fertilizer than indicated in the chart. Use the chart only as a general guide.
Since nitrogen is the element that needs to be applied most frequently and in the largest amount, we need to understand nitrogen deficiency symptoms in the fruit trees. They include pale, yellowish-green leaves; short, thin shoots; small, poor-quality fruit, and a general lack of tree vigor. There are also many other causes of similar symptoms.
Make sure what the cause is before you apply large amounts of fertilizer. Excessive amounts of fertilizer will cause poorly colored, late-maturing fruit that will not store well. Excesses often force trees into excessive vegetative growth and produce large numbers of water sprouts.
If you have grass as a cover crop around your trees, you'll need to apply about 20 percent more fertilizer to supply the needs of the grass, as well as to provide enough for the trees. Manures and mulches are great for adding organic matter to the soil, but add very little in terms of actual soil nitrogen.
Micronutrients are sometimes needed, but their use will be covered in a future column. Fertilizing fruit trees does not need to be a complicated process but it is a very necessary one. Apply the right amount of nitrogen now to ensure a good harvest. Avoid large applications of other fertilizers, particularly phosphorus, as they may tie up essential micronutrients.
- JOIN ME THIS SATURDAY morning from 7-10 a.m. on the KSL Radio Greenhouse show. The subject will be grasses in areas other than your lawn.
(Additional information) Graphic #1: Average shoot growth Average length of shoot growth, in inches, of healthy fruit trees.
Young Trees Bearing Trees
Type of tree (Up to 6 yrs.) (Over 6 yrs.)
Apple, dwarf and semidwarf 10-20" 4-8"
Apple, standard and spur types 10-20 " 6-10"
Peach, nectarine and apricot 10-24" 8-15"
Sour cherry and plum 10-20" 1-12"
Graphic #2: Nitrogen requirements
Pounds of nitrogen to be applied per fruit tree.
Age of tree Actual nitrogen Ammonium nitrate Ammonium sulfate
(34-0-0) (21-0-0)
1-3 years 0.25-0.5 0.75-1.5 1.25-2.5
3-8 years 0.5-1.0 1.0-1.66 2.5-5.0
Mature trees 1.0 minimum 3.0 minimum 5.0 minimum
Large apple 1.5-3.0 4.5-9.0 7.5-15.0
or cherry
Do not apply commercial fertilizers at planting time
© 1998 Deseret News Publishing Co.