Water is the single most essential resource for tree survival and growth. Drought conditions can lead to tree decline, pest problems, and non-recoverable damage. Drought stress may not kill a tree outright, but it can set it up for more serious secondary insect and disease infestations in following years.

The Mason Tree Committee offers these tips for watering your trees.

Why

Water is the single most limiting essential resource for tree survival and growth. Drought conditions can lead to tree decline, pest problems, and non-recoverable damage. Drought stress may not kill a tree outright, but it can set it up for more serious secondary insect and disease infestations in following years.

Healthy trees add value—to the homeowner’s property, and to Mason, a “Tree City USA”. It's an accepted fact in real estate that attractive and healthy street and landscape trees will improve the value of your home.

Where

Try to water the soil area that is directly beneath the foliage and shaded by the tree (under the drip-line).

Trees that have been in the ground from two to five years, and therefore have under-developed root systems, need additional watering care. For these, concentrate water over the root ball as well as the planting area.

Old, large trees can be extensively watered over the entire area under their foliage, but avoid the area three feet from the trunk base. The whole area below the foliage can be watered occasionally.

How

Slow, surface soaking allows tree roots more chances to absorb the water.

Manually, the best ways to water trees are by soaker hose or trickle (drip) irrigation that you turn on and off. A garden hose, if moved often, works well. It’s best to use a light organic mulch to conserve moisture, and apply water over the top of the mulch. Apply water across the soil surface and let it soak into the soil. Lay out water hoses or applicators out to the tree’s crown edge (drip-line).

How Often

Trees should be watered once or twice a week in the growing season if there is no rainfall in that week. Once you begin watering, you should continue to water until rain comes.

When

The best time to water is at night from 10 p.m. to 8 a.m. Trees relieve water deficits at night. Watering at night allows effective use of applied water and less evaporative loss, assuring more water moves into the soil and tree. This watering cycle minimizes pest problems.

The next best time to water is late afternoons, when foliage is dry and evaporation potential is not at its daily peak. Be sure to allow time for the applied water to dry off the foliage surfaces before the evening dew appears. This dry gap between watering and atmospheric condensation helps minimize pests.

How Much

A few higher volume waterings are much better than many, light, shallow waterings because light waterings encourage shallow rooting—which can lead to more severe drought damage.

Deep watering to a depth of 12 inches below the soil surface is recommended. Applying water deeper than this level misses the active roots and allows water to drain away from the roots.

Be sure the water soaks in well. Use mulch and slower application rates on slopes, heavy soils (clays), and compacted soils to assure water is soaking in and not running off.

For every 18°F increase in temperature, the amount of water lost by a tree and the site around it almost doubles. 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 water your tree should receive depends upon the tree size. A general rule of thumb is to use approximately 10 gallons of water per inch of trunk diameter for each watering. Measure the trunk diameter at knee height. The general formula is Tree Diameter x 5 minutes = Total Watering Time.

For example, when you hand water using a hose at medium pressure, it will take approximately 5 minutes to produce 10 gallons of water. If you have a 4” diameter tree, it should receive 40 gallons of water. When you multiply 4” by 5 minutes, you find that total watering time should be 20 minutes.

Fine soils (clays) require careful attention to prevent over-watering. Drought affects sandy soils more than others because water runs out of the rooting zone more quickly.

Much less water is required in the dormant season, but water can still be needed unless the soil surface is less than 40°F.

Many plants in a small area can compete within the soil to use any available water. This water competition can be severe.

For a limited time, the City of Mason will have tree watering bags for sale at the Mason Municipal Center. They will be available while the supply lasts for $15.75 per bag.

Posted June 22, 2007