What are the guidelines for watering trees and shrubs in summer, especially during a drought?
Trees and shrubs are important landscape assets, and trees are particularly important to the overall environment. In the event of a horticultural drought, decide to water your trees first, then shrubs, herbaceous plants, and finally lawns. Deep watering early in the morning encourages roots to grow deeply and strongly. It is best to use a soaker hose to reduce water waste and prevent disease problems by keeping the foliage dry.
When leaves droop and fold the plant is under stress and it is time to irrigate. It is best to water early in the day, when the evapotranspiration rate is lowest; leaves should be open to be capable of full photosynthesis during the day. Do not leave foliage wet at night, as this will encourage disease.
Courtesy of the NYBG Plant Information Service