Watering Trees

Source(s): Kim D. Coder, Professor of Community Forestry, Warnell School of Forestry and Natural Resources, The University of Georgia

Water is the single most limiting essential resource for tree survival and growth. Water shortages severely damage young and old trees alike, and set up healthy trees for other problems. Drought conditions can lead to tree decline, disease and insect problems and non-recoverable damage. Supplemental watering can greatly assist in maintaining tree health during droughts – both during the growing season or during the dormant season.

How To Water

The best ways to water trees are by soaker hose or drip irrigation. Automated lawn sprinklers are less efficient for applying water to trees than soaker hoses or drip irrigation. Even a garden hose, moved often, can provide a good soil soaking. Use a light organic mulch to conserve moisture and apply water over the top of the mulch. Do not allow water to concentrate at the base of the trunk as this can lead to pest problems.

Where To Water

Most of the tree’s absorbing roots are in the top foot of soil. Applying water deeper than this level misses the active roots and allows water to drain away, wasting efforts and water. Apply water across the soil surface and let it soak into the soil. Surface soaking allows tree roots more chances to absorb any water and helps maintain soil health.

Lay-out water hoses or applicators out to the tree crown edge (drip-line). Try to water the soil areas directly beneath the foliage and shaded by the tree. Do not water beyond the drip-line and do not water closer than 3 feet to the trunk base on established trees. Be sure the water soaks into the soil. Use mulch and slow application rates on slopes, heavy soils (clays), and compacted soils to assure water is soaking-in and not running-off. If the tree is surrounded with other landscape plants, or by turf, deep soaking applications will benefit all. Do not spray tree foliage when applying water. Water droplets on tree leaves can lead to pest problems and destruction of leaf tissue through sun damage. Try not to wet the trunk if possible. Young, newly planted trees need additional watering care. Water has limited horizontal movement in soil. You must apply water directly over where you need it in the soil. For new trees, concentrate water over the root ball, as well as the planting area, to assure survival.

Old, large trees can be extensively watered over the entire area under their foliage. Another method in watering large trees is to select roughly 1/3 of the area within the drip-line for concentrated water applications.

When To Water

The best time to water is at night from 9 p.m. to 9 a.m. Trees refill over the nighttime hours. Watering at night allows effective use of applied water and less evaporative loss, assuring more water moves into the soil and tree.

Because trees lose water from day-to-day, month-to-month, and season to season – dormant season watering during winter drought is important, especially for evergreen trees and juvenile hardwood trees that have not lost their leaves. Because of temperature and relative humidity interactions, much less water is required in the dormant season, but water is still needed. Do not water when the soil surface is less than 40°F.

For every 18°F increase in temperature, the amount of water lost by a tree and the site around it almost doubles. This feature of water loss must be factored into applying supplemental water to a tree. Trees surrounded by pavement and other hot, hard surfaces can be 20-30°F warmer than a tree in a protected, landscaped backyard. Water use rapidly climbs with increasing temperatures, and so should water application volumes.

How Much To Water

Depending upon soil texture 1 to 2 inches of water per week should keep a tree healthy. Trees in limited rooting areas, in containers or pots, or on major slopes, need additional care to assure water is reaching the root system in adequate amounts and not suffocating roots from lack of drainage. Five gallons per square yard is about 1 inch of water.

Fine soils (clays) require careful attention to prevent over-watering and root death. Sandy soils can be severely droughty because water runs out of the rooting zone quickly. Composted organic material additions and organic mulch covers on the soil surface can help hold and prevent rapid loss of applied water.

How Often To Water

Trees should be watered once or twice a week (minimum of 1 inch per watering)in the growing season if there is no rainfall in that particular week. A few heavy waterings are much better than many light, shallow waterings. A greater proportion of the applied water is utilized by the tree with heavy watering. Also, light waterings encourage shallow rooting which can lead to more severe drought damage. Once you begin watering you should continue to water until rain comes.

Center Publication Number: 220

Kim Coder
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