Few things are more delicious to bite into than an apple, warm with the sun and fresh picked from a backyard tree. Whether the apple is green, red or yellow, the crisp crunch of a ripe apple that you grew yourself has a certain satisfaction to it. Apple trees require a lot of care to perform well, and making sure they are fertilized properly is important to their overall health.
Direct observation is important to knowing if the apple tree is missing out on nutrients. A key measurement is the growth of the lateral branches. If the tree is receiving it's full and complete balance of nutrients the branches should grow between 12 and 18 inches per year according to Michael L. Parker, horticultural specialist at North Carolina State University. Other signs of a healthy, growing tree with plentiful nutrients are an overall height gain of 18 to 30 inches and nice looking, green leaves. If the leaves look small and discolored there might be a problem.
The only sure way to know if the soil is adequately nutritious is to have it tested for both the correct amount of nitrogen, phosphorus, and potassium, and the pH balance. Apple trees prefer a pH balance above 7.8, and when the soil is at that level then nitrogen is probably the only nutrient lacking. While the pH and nutrient-level balance can be done at home with an inexpensive testing kit, another revealing test is done in a profession lab. The analysis of an apple tree leaf from mid-summer growth shows the presence or lack of needed nutrients.
If you fertilize the apple tree, the best time is right as the flowers appear in the spring. If the pH is between 6 and 7.5 then an all-purpose 15-5-10 fertilizer will do fine. The numbers indicate the percentages of nitrogen, phosphorus and potassium in the fertilizer product. If the pH balance is high enough then only use a nitrogen fertilizer such as ammonium sulfate. Young trees need a special schedule for fertilization. If the tree shows 6 inches of growth in the first month after planting then scatter a cup of nitrogen fertilizer around in a 2-foot circle. The second season repeat the cup with a 3-foot circle, and then repeat again in April, May and June. The third and fourth year requires 2 and 3 cups, four times in the same schedule.
A mature apple tree with poor test results or growth should receive 1 lb. of nitrogen fertilizer for each inch of trunk diameter as the buds begin to open. Keep the fertilizer away from the trunk when scattering it, and under the tree drip-line. This can be repeated after the apple crop sets if it appears that there will be a significant crop. Otherwise the money spent on fertilizing the tree at this point is wasted.