University of Vermont Extension 
Department of Plant and Soil Science

Spring, Summer Article

By Dr. Leonard Perry, Extension Professor
University of Vermont

Trees and shrubs need moist, but not thoroughly wet, soil in order to grow well, resist insects and winter injury, and, in some cases, to produce flowers and fruit.

From early spring until about September 1, apply water adequately to all woody plants. Keep in mind that some, including cottonwoods, poplars, aspens, willows, maples, birch, spruce, and mountain ash, will need more water than others. Note, too, that except for evergreens, it is not advisable to wet the leaves, because this can encourage rust, blight, and mildew diseases.

After that, withhold water to allow the plant to harden off. This will reduce chances of damage to wood by early snowstorms and freezing temperatures. Then, in mid-October or prior to a ground freeze, apply water liberally several times to avoid winter drought.

How often should water be applied to established trees and shrubs?

During hot, dry periods, water your plants every six to 10 days. If the soil is very rocky, gravelly, sandy, or has poor water-holding capacity, water once every six days, but do not put on more than one inch per watering. For clay-loam soils, apply water every 10 days to two weeks, but put on about two inches of water per watering. Newly planted trees and shrubs need water every five to seven days.

To gauge how much water is applied, use a commercially available rain gauge or place a coffee can under the sprinkler. Check the time required to fill the can one inch deep with water. With this information you can calculate the time needed to put on more water and when to move the sprinkler or turn it off.

Be careful not to overwater, but be sure to put on enough to wet the ground to a depth of approximately 30 inches deep. You should wet the entire root area, which extends out at least as much as the limb spread.

Water well or not at all. Shallow watering will "starve" the deeper roots, causing more growth of the surface roots. In causing more root formation near the surface and less deeper down, you will predispose those roots to freezing conditions. Roots near the surface are not protected as well from the cold as are deeper roots.

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