We rely on trees to give for shade and cooling, but are we doing enough to help our trees survive the low desert heat?
Let’s take a look at some signs of heat stress and how to protect trees during peak summer heat.
How Heat Affects Trees
Trees move water through their roots, trunks, branches and leaves, then into the air through a process called transpiration; it’s similar to sweating in people. This is a natural process that keeps a tree healthy and growing. Heat increases how much water the tree loses during transpiration.
When a tree suffers stress from heat and loss of water, it is more vulnerable to disease or pest damage. Wounds on a tree trunk or branch are less able to heal because the tree is using all its energy just to stay alive in hot, dry weather.
Signs of Heat Stress
It can be difficult to tell drought stress from heat stress in a tree, especially when both weather elements strike the Phoenix area at the same time.
Wilting leaves typically are the first sign of heat or drought stress in trees and other plants. When a tree is under heat stress, it might fail to produce healthy-looking new growth. Interior leaves might turn yellow. The trunk can ooze sap, attracting ants or beetles.
How to Protect Your Trees in Summer
First, choose the right tree for your desert landscape (such as native trees like Palo Verde, Desert Willow and Acacia). Plant those most tolerant of heat and sun in areas of the yard that face south or west, the hottest summer exposures, or where there is reflection. Place trees less tolerant of heat on the north or east side of your home, or where the trunks get afternoon shade from houses, fences or other trees in summer.
Native and drought tolerant trees also typically experience less heat stress because these trees tend to fare better if they get less water than needed during especially hot weeks.
Water your tree more often if necessary, watering deeply with slow drips, not with sprinklers. If a tree is two years old or less, assume it might need more water during dry, hot periods. Otherwise, check the soil around your tree before choosing extra watering. Sometimes, too much water adds to the tree’s stress or chance of disease.
Painting young tree trunks, such as citrus, with white trunk paint (or household latex) can help prevent sun scalding and damage to the bark. Sun damage usually occurs on the trunk’s southwest side. You can shade young trees by moving a patio umbrella or shade cloth so it will screen some late afternoon sun hitting the young tree’s trunk.
Avoid overpruning a tree, especially one recently planted. Regular pruning improves a tree’s strength and health, but removing too many inner or upper branches can expose tender parts of the tree to more sun and heat. Be sure to complete pruning before new growth begins and well before hot months begin.
Your tree should perk up again when temperatures lower back to normal, so if the tree still looks stressed or unhealthy at that time, contact a Certified Arborist.