Fruit trees cannot thrive without an adequate supply of major, minor and trace nutrients. Apple and pear trees are powerful feeders and will often make satisfactory growth with no fertilizer, particularly in naturally fertile ground. However, properly fertilized trees will repay your investment with increased vigor, higher yields and greater resistance to pests and diseases.
Fruit trees need nitrogen for shoot growth and leaf production, which in turn affect the amount and quality of the fruit. For apples and pears, the recommended application rate is 0.1 lbs of nitrogen per inch of trunk diameter measured 1 foot above the floor and never over 0.7 lbs. You can provide 0.1 lbs of nitrogen together with approximately 0.5 lbs of ammonium sulfate, 0.3 lbs of ammonium nitrate, 0.8 lbs of blood meal or 1.5 pounds of cottonseed meal.
Potassium and Phosphorus
Apple and pear trees have extensive perennial root systems that are normally able to absorb enough potassium and phosphorus from the pure supply in the soil. If your land is deficient in potassium or phosphorus, applying approximately 0.4 lbs of phosphate or 0.2 lbs of potash per tree will help. You can offer the phosphate with 0.9 lbs of triple superphosphate or 3 pounds of bone meal, or the potash with 0.4 lbs of potassium sulfate or 4 lbs of wood ash. Surface applications of phosphorus are ineffective, so mix phosphorus fertilizer into the soil around the tree.
Apple and pear trees need small quantities of many different nutrients, such as boron, iron, zinc and manganese. If your trees exhibit signs of a specific deficiency, you may look for a fertilizer product for this particular element. Generally, however, the simplest approach is to fertilize your trees with a broad-spectrum mineral amendment such as greensand or azomite. Mix these products into the ground at a rate of about 5 lbs per tree.
Soil pH Levels
The pH scale is used to quantify acid and alkaline levels in your land. Nutrients in the soil become more accessible to a plant when the soil pH is within the scope preferred by that specific plant. For apples and pears, the appropriate pH range is 6.0 to 6.5, or slightly acidic. The only reliable method to accurately adjust your pH is to get a soil test that reports pH and offers amendment recommendations that are suited to a soil and growing conditions.