Lime in an alkaline substance that will decrease the acidity in soil by increasing the pH balance. Apple trees need a pH balance of 5.8 to 6.9, according to Clemson University. While lime should be added to soil before the apple trees are initially planted, more lime can be added later as the trees mature. A home soil test will allow you to determine how much lime you should add to your soil.
Test your soil around the apple trees to determine the pH of the soil. For a lower pH, around 4.0 to 4.9, add 1.36kg. of lime per tree. For a pH of about 5.0 add 0.907kg. per tree. For a pH of 6.0 add 0.454kg. per tree.
Till the soil gently around the base of the apple trees with the rake in order to loosen up the soil.
Sprinkle the lime onto the soil around the apple trees in about a 5-foot diameter from the trunks. Keep the lime about 6 inches from the trunk of the trees. Work the lime into the soil to a depth of 3 to 5 inches.
Add lime to mature apple trees in the spring and fall every other two to three years to keep the soil pH balanced. Lime takes several weeks to months to decrease the acidity of soil.