Fruits, being largely water and sugars, remove relatively few nutrients from the soil, compared to other crops. Therefore, much of the nutrients a fruit tree needs can be met through decomposition of mulch (if you mulch your trees), or by the application of lime and organic soil ammendments used when planting the tree.
Supplementary fertilization may still be required for optimal growth and production of fruit. Doing a soil test can indicate what elements and nutrients may be deficient in your soil. Many Local Cooperative Extension Services provide soil testing services, or foliar analysis. Foliar analysis actually works better for fruit trees. If you are serious about fruit production, it is best to have the soil or foliage tested at least every year or two.
You can fertilize your fruit trees either organically, or with commercial fertilizers.
Fertilizing A Newly Planted Fruit Tree
Use a weak solution of Fish Emulsion as a starter fertilizer, or a pinch of bone meal may be added to the planting hole, but do not add commercial fertilizer.
Fertilizing Established Fruit Trees Organically
Most organic fertilization programs focus on supplementing nitrogen as the key element, since it is needed in the greatest amount by the fruit trees. If you have only a few trees, and you want to fertilize them organically, buy a bottle of Fish Emulsion at your local nursery and garden center. You may also use granulated organic fertilizer, such as those that contain chicken manure or other organic substances.
Apply organic fertilizer (at rate recommended on label) by hand or with a rotary type spreader around the drip-line of the tree about 3 to 4 months prior to harvest date. If you make your own organic compost, simply use it as a mulch around the the drip line to a point 12″ from the trunk. The nutrients will seep down into the soil where they can be picked up by the root system.
Fertilizing Established Fruit Trees With A Commercial Fertilizer
To fertilize a fruit tree with a commercial fertilizer, such as 10-10-10, toss a thin circle of pelletized fertilizer around the trees “drip line,” which is the part of the soil below the outer perimeter of the branch system. Follow instructions on product label for proper application rates and methods.
During the first year after transplanting, spread fertilizer after new growth has emerged in Spring. If using 10-10-10, spread about 1 pound of per inch of trunk diameter. Then work the fertilizer into the soil with a trowel, and mulch – making sure you keep the mulch at least 12 inches away from the trunk of the tree.
In each subsequent year, make a split application: half after new growth has emerged in Spring, and the remaining half at a month later, using 10-10-10 at the rate of 1 pound per inch of trunk diameter. Trunk diameter is measured 12 inches above the ground.
Or, you may substitute 10-10-10 with the following: Spread a 6″ band of calcium nitrate within the dripline of branches, at a rate of 2/3 pound per 1″ of trunk diameter, and broadcast sulfate of potash-magnesia (sul-po-mag) at 1/2 pound per 1″ trunk diameter.