Retaining a long-lasting tree means proactively ensuring it has what it needs to thrive. The drip line – an imaginary circle on the ground directly under the outer edge of the leaf canopy – is where the tree gets moisture and nutrients.
With excess water, roots will suffocate; without water, most roots dry out and die. Trees in lawn areas often get too much water because trees and grass have different watering requirements.
Your tree's soil, the amount of competing grass around your tree, and the local weather conditions dictate how much water to give your tree and how often. In general, trees need the equivalent of one inch of rainfall per week from June through September, but trees use water even during winter.
Before you water, examine the soil moisture two to four inches deep. If the soil feels dry or just slightly damp, it needs water. Well-drained, sandy soils will need water more often than a loam or clay soil.
Newly planted trees require routine and thorough watering for at least three years after planting, particularly during dry summer months. Avoid short, frequent watering, which promotes development of a shallow root system that is more vulnerable to drying out and other stresses. The best way to water a newly planted tree is to place a garden hose at the base of the tree. Run a slow trickle of water for several hours or until the soil is thoroughly soaked. To help hold or direct the water around the root system, build a temporary soil berm or saucer. Remove after one year.
Using mulch around the base of the tree is an important part of long-term tree care. Mulch keeps the soil moist, limits weed growth, and discourages injury from lawnmowers and weed-eaters. Wood and bark chips are good mulching materials. You can use a porous landscape fabric as a weed barrier underneath the chips, but don't use plastic because it suffocates the roots. You can also use fallen leaves to mulch your deciduous trees.
Apply a three- to six-inch layer of mulch and spread it to form a circle the size of the drip line. For new trees that haven't yet developed a mature canopy, mulch with a ring of wood chips extending out two feet from the base of the tree.
Keep the mulch from direct contact with the tree trunk. Some bark mulches may contain pathogens or contaminants that can harm your trees. Keep mulch at least six to eight inches away from the trunk of a tree to prevent fungus diseases and to allow for maximum air circulation.
Maintain the mulch ring on a regular schedule to keep grasses from competing with the tree. As the tree continues to grow larger throughout its life, its drip line will move further out, requiring a larger circle of mulch.
If you plan to have chemicals injected or implanted in your trees, make certain that it is done only by highly skilled professionals. Check injection and implant holes after one season to make certain they are closed. Injection and implant holes should be very small and shallow at the tree base, not in the roots.
Depending on the makeup of your soil, your trees may flourish with the addition of nitrogen, phosphorus, potassium, calcium, magnesium, and other macro- and micro-nutrients, referred to as a group as fertilizer. Slow-release nitrogen fertilizer is often the best option.
Fertilize every two or three years in the fall after the leaves have dropped or in early spring before growth begins. Never apply nitrogen in late summer because it can stimulate new growth that may not harden off or go into fall dormancy properly. This new growth will be more easily damaged by early fall frosts.
Apply the fertilizer directly to the soil surface, and water it in. If there is thick grass sod beneath the tree, use a pipe to punch holes 12 inches deep in the sod beneath the drip line of the tree and apply the fertilizer in the holes. This helps the fertilizer reach the tree's root system.
Avoid using "weed and feed" fertilizers in the drip line of your tree. Excessive amounts of fertilizer should be avoided. Don't fertilize trees that have been planted for less than a year, are past maturity, or have turned color for the fall season.