Newly planted and young trees need the most water assistance during drought conditions because their root systems are not as expansive as large, mature trees. New and young trees should be monitored for water for the first three years. It is important to water deep, not shallow.
Even when a summer rain shower occurs, the dry soil above the roots must first become saturated before much of the root system gains access to the water. Further, grass or lawn above the tree roots also soaks in part of the precipitation. Mature trees should be watered once or twice a month during drought conditions. Use a shower-like attachment or a plain hose to apply the water.