If you have one or more apple trees (Malus spp.) in your garden, you're probably looking forward to an abundant and flavorful crop. It's important to give apple trees proper care to ensure they produce as many apples as possible and that these are free of damage. Fertilizing trees each spring helps ensure this, as does giving some basic care during the season and being proactive to prevent problems from pests and diseases. Apple trees usually in U.S. Department of Agriculture plant hardiness zones 3 through 8, with some variation among cultivars.
Watering and Fertilizing
If you have a newly planted tree or one in its first year or two in the ground, it's important to give the tree adequate moisture to promote good growth. A new tree needs about one gallon of water every seven days during the growing season. Even a large, mature apple tree can use many gallons of water on a hot summer day, so moisture is critical to keep the tree healthy. Provide extra water whenever the top inch or two of the soil under the tree feels dry, but provide water through drip irrigation or a soaker hose and allow water to soak in slowly. These methods also keep foliage dry to help prevent growth of fungal organisms.
How to Fertilize
Fertilizing an apple tree each spring helps it grow and produce the maximum number of flowers, along with lots of fruit later in the season.
Identify the tree's drip line -- the circular area just under the tree's outermost branch tips, where roots that take up water and nutrients are found.
Place the empty bowl on the scale, then scoop fertilizer into the bowl until the scale registers additional weight equal to the amount you need. Use 1/2 pound for each year of a tree's age. For example, use 1 pound for a 2-year-old tree and 2 1/2 pounds for a 5-year-old tree; for a tree that's 15 years old or older, use 7 1/2 pounds.
Using your gloved hand, evenly scatter the fertilizer on the ground -- called broadcasting -- around the tree, at its drip line.
Pruning Apple Trees
It's important to prune a young apple tree, so that it develops into a well-shaped tree capable of bearing abundant fruit. If you've planted a new tree in the spring and it has one central stem, cut back it's main stem -- called heading back -- so that it's only 24 to 30 inches tall, removing any broken or damaged branches at the same time. Also cut back any side branches so that only one or two buds remain on the branch. It's best to do this immediately after planting, to encourage new branching at the cut points. Use sharp pruning shears, wiping them with rubbing alcohol after each cut to prevent spread of plant disease.
For a more mature tree, it's best to prune while it's dormant, either in winter or in very early spring, before new growth starts. It's also safe to prune in early summer, especially for a tree with lots of extra growth, but summer pruning can slow ripening of fruit and removes leaves needed for nutrient production.
Prune a young tree heavily for its first three years, to encourage bushy, vegetative growth that supports fruiting later in the tree's life. Remove thin, vertical branches, called suckers, at their origins. Branches that grow horizontally, at a 45- to 60-degree upward angle, eventually produce the most fruit, so retain most of these. Remove any damaged or diseased branches, along with some branches that grow at narrower angles -- less than 45 degrees. These are called a weak crotch because they tend to be weak and bear little fruit. Also remove or trim back some branches to allow light to enter the center of the tree.
A mature apple tree also needs annual pruning. Remove any branches that are damaged, or that cross and rub on each other, because injuries provide an entry point for pests and disease. Generally thin the branches to allow light into the tree's interior, removing those that have weak crotches.
Avoiding Pests and Diseases
Apple trees are susceptible to several fungal diseases. For example, powdery mildew causes white, fluffy growths on leaves and buds, while white rot causes brown, rotting spots on fruit and can also cause soft, brown spots, called cankers, on stems. These problems are best controlled by removing dropped leaves and fruit from under the tree regularly. If you mulch under an apple tree, keep the mulch back 5 or 6 inches from the tree's trunk to prevent fungal growth.
Several pests could also infest an apple tree, including apple maggot flies that lay eggs in summer on apples; emerging larvae tunnel into apples and feed on the fruit. The coddling moth also lays eggs in the fruit and resulting larvae can destroy the fruit. To control larval pests, spread a tarp under the trees in the morning and shake the branches to dislodge them, then dispose of them. Rake up and discard any dropped fruits and remove damaged ones from the tree, to prevent spread of the insects. Spraying a natural bacterial control called Bacillus thuringiensis on the tree about 15 days after petals fall and again five days later also helps destroy some of these pests. Dilute the product at a rate of 1 ounce per gallon of water, but also check your product label for further directions.