A dry winter, minimal spring rains, record high temperatures and low summer precipitation puts extreme stress on woody plants. The stress increases susceptibility to insects and disease.
Trees and shrubs should be thoroughly watered if they begin to show signs of leaf wilt, discoloration or drying, especially at leaf edges.
Trees are able to obtain moisture longer than most other plants due to deeper roots, so symptoms of drought stress tend to be more delayed and some symptoms may not appear for months or even years.
Newly planted trees are particularly at risk during prolonged dry periods, but even trees that have survived harsh conditions in the past can decline or even die from extended drought and heat.
When it doesn't rain for days on end, some plants just won't make it without supplemental watering. Sprinklers help, but they waste much more water than some type of drip method of watering. Water that is applied slowly and gradually has much less potential for evaporation than water that's applied through overhead irrigation. Water sprayed through hot air is obviously going to evaporate more than water entering the soil directly.
Not everyone can afford a drip system, but soaker hoses have improved to the point where they are almost as efficient as the expensive drip systems used by commercial plant nurseries.
Most are made out of nylon, which allows them to be flattened and rolled up in a way that is much more compact than the porous, rubber types. This nylon material makes it much easier to store the hose when it's not in use and it makes it easier to wind the hose through whatever plant material you are trying to water.
Damage to a tree or shrub caused by drought stress becomes a permanent part of the plant. If that type of damage is allowed to occur repeatedly over a number of years, eventually the cumulative effect becomes more than the plant can handle. At that point, the plant dies, no matter what you do.
If you have a favorite shade tree that took years to grow, then heed this advice: Don't let it suffer from drought. A soaker hose ringed around the tree can provide lifesaving water to the tree during times when it needs it most.
To check soil moisture in a tree's root zone, push a long screwdriver into the soil a foot or two out from the trunk. If the ground is dry and in need of watering it typically is difficult to push the screwdriver in more than a few inches.
If the soil is dry, a deep, thorough watering will provide the most benefit to trees. One of the best methods is to coil a soaker hose around the tree several times from the trunk to the drip line and let it run until the soil is moist to a depth of 8-12 inches.
Five gallon buckets with holes can also be used to slow-irrigate the soil under trees.
The soil type does affect watering. Sandy soils have to be watered more frequently. Clay soils can be hard to re-hydrate once they dry out but will retain moisture longer.
It is also important to have 2-3 inches of mulch under trees to conserve moisture and insulate the soil from high temperatures. Unlike turfgrass, mulch doesn't compete with the tree for nutrients and moisture.
Some symptoms of drought - stunted or distorted foliage - are similar in appearance to herbicide damage. High temperatures can cause herbicides like 2,4-D to volatize and change from liquid to gas. As a result, the herbicide doesn't bind to soil particles but rises and spreads to trees and shrubs where it damages and distorts the foliage.
Applying herbicides and/or fertilizing during extreme heat is more likely to cause damage to plants than to provide assistance.