Watering plants during dry spells wastes time and water, increases the chance of spreading disease in the garden, and may actually decrease your plants’ chances of weathering a drought.
Most people water with an overhead sprinkler system or hose. Better than nothing, perhaps, but wetting the foliage of plants increases the chance of spreading disease. If you must wet the foliage, do so in the morning or early afternoon to allow time for the plant to dry off before evening. Applying water to the root zone via drip irrigation, soaker hoses or just letting a hose trickle at the base of the plant is better.
Give plants a good soaking once a week or every 10 days rather than a shallow watering more frequently. Watering deeply encourages a plant to send its roots deep into the soil; shallow watering causes a plant to keep its roots at the surface, where they become more vulnerable to drying.
Remember, too, that mature trees can withstand a moderate drought, but trees planted within the last three years should get water during dry spells. The general rule is to give a tree about 10 gallons of water per inch of trunk every week to 10 days if Mother Nature doesn’t turn on the waterworks.