Random Thoughts Regarding the Desert and Our Hot Summer

Perhaps this summer has been brutal but plants like palo verde can handle “brutal” weather. 

 "Native" palo verde in Arizona in bloom

Be careful how these plants are pruned. The tendency is to prune them too high and this removes the shade that the tree naturally provides the trunk and limbs. Watering also helps. Plants like palo verde respond very nicely to increases in applied water very quickly..in just a few days. Water these plants with a hose to give them a shot of water and improve shading of the limbs and trunk. 

 

Sap coming from Palo Verde. Removing too many branches and exposing too many large limbs and the trunk can lead to sun damage of this thin barked tree.

Hopefully plants like palo verde were not pruned to allow excessive sunlight to shine on the trunks and limbs. Also, water in the soil helps keep limbs and the trunk from burning because these areas release water to the air and help cool the limbs and trunk through evaporation of water from microscopic holes that can open and close called stoma or sometimes called stomates. If water is restricted it cannot cool itself properly and they will burn. OR water loss can be faster than the plant can replace…as in the case of apple fruit…and burning occurs.

That is a wide variety of plants to have sunburn on. Sunburn on trees is usually restricted to trees with a think bark (palo verde fits this) and a lack of shade covering the limbs and trunk. Sunburn is on the sides of the trunk and limbs that face the sun and not on the other sides in the shade. If this damage extend into the side in the shade then it is something other than sunburn that is going on. 

 

In my opinion too many of the lower limbs were removed on this Palo Verde which can lead toward sunburn

You can apply the same logic to agave and desert spoon. Not enough water can contribute to sunburn. If they are droughty then will burn more easily than if they are getting enough water. 

A lack of soil improvement…poor soils that were not improved by adding compost at the time of planting…YES, this includes cacti!...may sunburn or turn yellow from intense sunlight. Sunburn comes in different degrees of severity…mild sunburn is a yellowing of leaves or fruit but not death of the plant tissues  beneath the damage. Medium damage results in yellowing with some brown or tissue death in or near the center of the yellowing…there is tissue death and this tissue death will attract bugs and other critters that sense the plant is damaged. 

Borers will attack sun damaged areas on the trunk and limbs of trees

These are bugs that are “decomposers” who want to break down these damaged plants and “recycle” them…naturally. The third stage is death of the tissues facing the sun, not only brown but cankered with bark or the skin dead and scaling or peeling back. This makes a pretty ugly plant. But the sides away from the sun are not damaged and the plant will survive unless some “decomposers” get in their and try breaking them down by feeding on them. Borers are in this category. They are goners if they look bad enough you cant live with them any longer. In most cases they will survive.