Fertilizer for Fruit Trees

Without adequate nutrients, fruit trees do not grow well and are unlikely to produce good fruits. If you want a healthy, flourishing tree with an abundant crop, you'll have to add yearly fertilization to your regular maintenance schedule.

Nitrogen is the most important nutrient for fruit trees, and the only one you need to look at when figuring application rates for different types of fertilizer. The percentage of nitrogen in a fertilizer is represented by the first number in the N-P-K ratio. A fertilizer with an N-P-K ratio of 10-5-5, for example, contains 10 percent nitrogen, and 5 percent each phosphorous and potassium.

The exact nutrient content varies depending on what type of fertilizer you use. Every fertilizer sold lists the N-P-K ratio on its packaging. You can also apply nitrogen-containing chemicals and organic matter based on their nitrogen content.

Fast-release fertilizers make the nitrogen available quickly and only last a few weeks in the soil, while slow- or medium-release fertilizers make smaller amounts of nitrogen available over a longer period and are usually a better choice for fruit trees.

Urea, 46 percent nitrogen, fast release rate.

Ammonium nitrate, 34 percent nitrogen, fast release rate.

Blood meal, 15 percent nitrogen, medium release rate.

Cattle manure, 0.5 to 1.5 percent nitrogen, medium release rate.

Compost, 1.5 to 3.5 percent nitrogen, slow release rate.

Feather meal, 16 percent nitrogen, slow release rate.

Fruit trees need to be fertilized only once every year. Fertilize newly planted trees three weeks after planting, and established trees one month before new growth starts in spring. With new trees, apply fertilizer starting 10 to 12 inches away from the trunk and out to the edge of the drip line. With established trees, apply fertilizer from a couple inches away from the trunk to the edge of the drip line. The drip line is the point on the ground directly underneath the outer edge of the branches.

Apply fertilizers directly to the soil beneath the trees. Unless the fertilizer packaging specifically instructs you to work fertilizer into the soil, simply scatter it evenly across the soil under the tree.

After fertilizing, water to move nutrients deeper into the soil. Water enough to soak the soil, but not enough to cause water to start draining away across the soil surface instead of sinking into the ground.

Though ideal application rates can vary based on the tree's age, annual growth rate and the species of fruit tree, a standard application rate will work in most situations. For most fruit trees, apply 0.10 pound of actual nitrogen per year the tree is old or for each 1 inch of trunk diameter. Stop increasing the application rate when trees are 10 years old or have a 10-inch-diameter trunk, so you never apply more than 1 pound of actual nitrogen per tree. Cut these application rates in half for pears (Pyrus spp. U.S. Department of Agriculture plant hardiness zones 4 through 9).

Because this application rate is based on actual nitrogen, how much fertilizer you apply depends on the type of fertilizer you choose. To find the application rate for your fertilizer, divide the pounds of actual nitrogen you need by the percentage of nitrogen in your fertilizer.

For example, if you need to apply 0.50 pound (1/2 pound) of nitrogen and your fertilizer contains 16 percent nitrogen you'll use the formula: 0.50/0.16 = 3.13. The result means you'll apply about 3 pounds of fertilizer.

As another example, if you apply a fertilizer that contains 10 percent nitrogen, you'll need to apply 1 pound to a tree that's 1 year old, but 10 pounds to a tree that is fully grown and requires 1 pound of actual nitrogen per year.

Occasionally, fruit trees require additional trace elements like iron, calcium and zinc. You can find out which nutrients your soil lacks by conducting a soil test, or you can apply trace nutrients whenever you notice signs of deficiency in your trees.

Iron deficiency shows up as yellowing on the leaves near the ends of the branches. The leaves turn a pale color with bright green veins, and occasionally develop crispy brown edges.

Treat by applying chelated iron to the soil in amounts based on the tree's size. For example, a product containing 5 percent iron uses 3 ounces of chelated iron per 1 inch of trunk diameter as measured 4 1/2 feet above the ground. Mix the required amount with 2 gallons of water, then pour this solution over the soil under the tree's drip line. To prevent problems in the future, add organic matter to the soil and avoid over-watering.

Lack of calcium causes brown spots on the fruits. These spots can be up to 1/2 inch in diameter and show up around harvest time, so you'll have to wait until next year to treat the plants.

Treat by mixing 2/3 ounce calcium chloride in 1 gallon of water, or according to label rates. Pour the mixture into a garden sprayer, and use that to spray the leaves until they are completely covered with liquid. Make three applications in the summer, each one month apart.

Trees deficient in zinc develop small, narrow yellow leaves with dark green veins.

Apply zinc in the spring before leaf buds start to unfurl at a rate of 1 tablespoon of zinc sulfate in 1 gallon of water. Using a garden sprayer, spray the tree branches until they are thoroughly soaked.