Drip irrigation in New Mexico vineyard, 2002 Drip irrigation in New Mexico vineyard, 2002 (Photo credit: Wikipedia)

During the long hot days of summer irrigate as needed to provide the equivalent of 1” of rain per week (enough water to saturate the soil to 1 foot deep). Irrigation is especially valuable for newly planted trees (1-2 years) whose root systems are not fully established deep into the soil. Mature fruiting trees will also benefit from irrigation in the last few weeks before the fruits are ready to pick. Water in the tree is used to fill and expand the cells in the fruit. Extra water will pump up the fruit so it is large and juicy when you pick. During extreme heat episodes, a little more water than you are accustomed to applying may be needed to reduce signs of heat stress in your trees such as excess early fruit drop, leaf wilt and leaf curl. It is important to provide the water to the portion of the root system that will take it up. Apply the water to saturate the soil from just inside the leaf canopy to several feet beyond the drip line. Avoid wetting the foliage and fruit of fruit trees that are sensitive to brown rot, powdery mildew, and other fungal diseases. Drip irrigation allows you to use less water, keep the foliage dry, and still accomplish the goal of maintaining your trees.

As plants start heading into dormancy later in the month, or early September, you can begin to water less frequently, but don’t let plants get too dry. Plants whose inner or lower leaves turn yellow and drop are likely showing a drought stress response, as oldest leaves are shed when water supply becomes short. If drought becomes severe, early fall color and total leaf drop can occur. A word of caution: These very same symptoms can show up when excess water in the planting hole drowns roots (displaces oxygen from the soil). This can even occur in a well-drained soil, if the soil in the planting hole was significantly modified at planting time. Dig below the surface. If you find waterlogged soil that smells bad, you probably need to correct soil drainage or your watering practices.