One of the great virtues of trees is that they take relatively little care once they have been planted. If a tree does well in our climate, is planted in an appropriate location, and is healthy when planted, then there is a good chance the tree will thrive and eventually require little care.

There are, however, a few essential steps to make sure your tree succeeds. Proper care is particularly important for the first five or so years after the tree has been planted. During this period, the tree is still establishing its root system, is relatively weak, and is becoming acclimated to its site. This article describes the five essential steps: watering, mulching, watching for disease and pests, providing support, and pruning.

Water. The most important step is to make sure the young tree receives adequate water. A tree transplanted from a five-gallon pot has a limited root system. In our Mediterranean climate, with its hot and dry summers, a young tree must be watered during the first few years while its root system develops.

Trees need deep watering. To be effective, the soil should be saturated to a depth of 12 inches below the soil surface. The soil should be saturated within the entire “dripline” of the tree. The dripline is the entire area beneath the outer edges of the tree’s branches. For evergreens, water three to five feet beyond the dripline on all sides of the tree.

Saturating the soil beneath the dripline takes time. If the water pressure is too high, water will flow into the gutter or away from the tree before the water gets the chance to saturate the soil. Watering for short periods of time only encourages shallow rooting, which can leave the tree vulnerable to drought. The objective is to water slowly, dispersing the flow of water to get the water deep down to the roots. Lawn sprinklers do not provide the sort of deep watering that trees require.

Do not dig holes in the ground in an effort to water deeply, because holes tend to dry out the roots. Overhead spraying of tree leaves should also be avoided because it is inefficient, wastes water and encourages shallow root systems.

Some garden stores sell “soil needles” and “deep root feeders.” These devices are attached to the end of a hose and sunk into the ground. They are an effective means of making sure that water penetrates the soil. Work the needle into the soil at an angle to a depth of eight inches. Use the needle at low to moderate water pressure. Water the area under the branches. Scatter the sites around the area bordered by the drip line. For new trees and those planted within five years, place the needle three or so feet from the trunk. Water a minimum of four sites around young trees.

A deep soaking from a garden hose on low pressure also works well. Move the hose around the base of the tree, two or three feet from the trunk. It is also helpful to use soil to build up a “watering well” around the base of the tree. The well should line up with the tree’s dripline.

The amount of water your tree should receive depends upon the tree size. A general rule of thumb is to use approximately ten gallons of water per inch of trunk diameter for each watering, measuring trunk diameter at knee height. A hose at low pressure produces roughly one gallon of water per minute. So if your tree has a trunk with a four-inch diameter, the tree should be watered at low pressure for roughly 40 minutes. These numbers are not exact, but they provide a rough guide to the amount of water required.

Trees should be watered from April through September.  Watering should occur twice a month during this period – three times per month during the hottest summer months, when temperatures climb into the upper 90s or low 100s.  Winter-time watering is generally not required, but it is a good idea to keep watering until the first winter rains arrive.

If a tree is not receiving enough water, the tree may exhibit the symptoms of “drought stress.” Drought injury symptoms on tree leaves include wilting, curling at the edges, and yellowing. Deciduous leaves may develop scorch, brown outside edges or browning between veins. Evergreen needles may turn yellow, red or purple. They may also turn brown at the tips of the needles and browning may progress through the needle towards the twig. In continued drought, leaves may be smaller than normal, drop prematurely or remain attached to the tree even though brown. A tree that is under drought stress should not be fertilized, since the salts in the fertilizer may burn the tree, and fertilizer encourages leaf growth that a stressed root system may not be able to support.

Mulch. Applying mulch is a great way to keep soil moist and to control weeks.  Mulch around your tree with approximately four inches of organic mulch. Pull mulch back six inches from the trunk of the tree so that the soil around the trunk is exposed.  Wood chips, shredded bark, leaves, evergreen needles and yard clippings all serve as good mulch. Avoid using stone or rock; these materials heat up in the sun and dry out the soil.

Fertilize. Urban landscape trees may be growing in soils that do not contain sufficient available nutrients for good growth and development. In these situations, it may be necessary to fertilize to improve plant vigor. Often, time-release fertilizers are placed in the hole at the time the tree is planted. In those instances, young trees are unlikely to require supplemental fertilizing. Applying a light fertilizer once a year or so, however, may help the tree thrive. Check with a local garden shop to determine the right fertilizer to use based on soil conditions and the type of tree in your yard, and be sure to avoid over-fertilizing. 

When you apply a broadleaf herbicide to your turf, remember that tree roots coexist with turf roots. The same herbicide that kills broadleaf weeds in your lawn is picked up by tree roots and can harm or kill your broadleaf trees if applied incorrectly.        

Watch for disease and pests. Young trees are particularly vulnerable to disease and pests. The best way to avoid these problems is to select a variety that is resistant to diseases that are common in our area. In addition, keep a plastic collar around the base of the tree in order to protect the trunk from damage from rodents, weed trimmers or stray soccer balls. 

Support. Young trees have thin trunks and need support against the strong northwest winds that sweep through our area on a regular basis. The best way to provide support is to pound two sturdy bean poles on either side of the tree, and then tie the tree to the poles using thick garden tape or tree support cords. Make sure the ties are taught enough to provide support, but not so tight that they girdle the trunk.  In our area, the poles should be to the east and west of the tree, so that the north winds do not bang the young tree into one of the posts.

Prune. Young trees to not require much pruning. Dead limbs should be removed. So should limbs that cross one another, or that make a tree out-of-balance. Some trees tend to produce dense branches and foliage, and it is a good idea to thin trees like this so that they do not get knocked down by a stiff wind. Young trees should be pruned lightly, but never remove more than 25 percent of a tree’s canopy.  The best time to prune is after leaves have dropped, before spring leafing.

Trees increase property values, cool our urban streets, reduce energy use, and make our town’s streetscapes more beautiful. Obtaining all these benefits through proper tree care requires only modest effort.