Woody omamental trees and shrubs have deeper, more extensive root systems than turfgrasses or herbaceous omamental plants. The root system of a mature tree, for instance, extends two to three times the canopy spread. Woody plants can therefore extract moisture from the soil even when the soil surface appears bone dry, and they can survive long dry periods without supplemental irrigation.

Use drip irrigation on trees and shrubs in the water-use zones of the landscape. Locate the emitters within the drip zone line of plants where the concentration of absorbing roots is the highest. During extended dry periods, operate the system 1 to 2 times per week. Run the system long enough to thoroughly wet the soil 6 to 8 inches deep. Regular and thorough watering of newly planted trees and shrubs encourages good root establishment and greater drought resistance.