Drought conditions throughout our area in 1999 have created serious problems for our older mature trees. Single trees isolated on a lawn or park setting are more susceptible to damage caused by a lack of natural rainfall such as last year. Most urban trees are under stress from the drought even if they look healthy.
Water is required for all biological processes of plants and trees. When there is an adequate supply, water seeps down through the soil, gradually saturating each layer. Trees depend on water and moisture in the upper layers of soil — usually the top 6 to 12 inches where the root system is located. In severe drought conditions, more water is required to keep the upper layers of soil moist. The first signs of water stress in shade trees is leaves wilting, turning color, curling, and eventually dropping off the trees. Remember these trees are stressed, not always dead. Many will survive.
To help correct this situation, mulch 2 to 4 inches of mulch around trees, no mounding high on trunk, spread under canopy. This conserves soil moisture. Aeration and fertilization can help these trees with the rain we have had this year. Water in evenings. Lower temps results in less evaporation. Water only if there is not adequate rainfall. Remember light watering creates shallow rooting.