Trees Suffer During Prolonged Drought

Posted: 12:51 PM, Aug 15, 2018
Updated: 2018-08-15 16:51:44Z

August is usually hot and dry – with the exception of the all-too-frequent sudden thunderstorms – and brings about a certain lethargy when it comes to yardwork.

"Who wants to work outside in this heat?" you may ask as you languish in the shade of a tree with a pitcher of mint juleps.


But even to have that shade oasis growing healthy in your landscape, it is important to take some simple proactive steps to ensure its longevity – especially during times of drought.


"While it's impossible to keep every tree in good health during severe drought, taking a proactive approach for a prized tree or one for which you have sentimental attachment can prevent long-term damage," advises Tchukki Andersen, CTSP, BCMA and staff arborist with the Tree Care Industry Association. "A tree that is supported with good cultural practices, preemptive monitoring for pests and diseases, and appropriate responses to warning signs will have an increased chance of survival."


Silent Suffering: Drought damage starts beneath the soil line, in the form of root damage, long before any outward signs of trouble. After a tree's unsuccessful attempt to conserve water by closing leaf stomata (pores), its feeder roots die back, sometimes so drastically that the tree is unable to absorb enough water to support itself. Such drought stress may lead to tree death, but usually the signs of stress are much less dramatic. "Leaves are undersized and may wilt, yellow, curl or crinkle, and may be marginally scorched or even turn brown and drop early," explains Andersen. "Emergent shoots are short. In an effort to right the imbalance caused by root-loss, crown dieback or a general thinning of the canopy occurs."


Opportunistic pests and diseases: This is when "opportunistic" pests make their move. Boring insects are thought to be drawn to the chemical and acoustic signals of stressed trees. The sound of the tree's breaking water columns cues the borer to invade the tree and lay eggs. Andersen recommends applying a 3-inch layer of composted wood chip mulch on the ground over the root zone at least out to the drip line (the ground under the outer edge of the branch spread). This will hold moisture longer for stressed roots to access, and will provide a long-term nutritional source for the soil. Prized or important trees may be protected from wood-boring insects with spray or injection chemicals, but they should be treated before becoming drought-stressed.

Stressed trees are also vulnerable to fungal pathogens. Andersen notes that when a chemical change in the tree signals a weakened state, certain pathogens penetrate the bark and cambial zone (tissues responsible for secondary growth of stems and roots) with fan-like, leathery clumps, cutting off the tree's water supply.


While all trees are at risk during long periods of drought, some are more susceptible to its effects. New transplants are highly vulnerable to drought stress, so supplemental watering for the first few years of establishment is necessary, to the extent that it is allowed. Trees already under stress, such as those on dry slopes, surrounded by pavement or improperly planted, are at high risk of decline.

Watering trees deeply with soaker hoses or irrigation systems – as opposed to brief, surface watering – helps sustain trees. But with so many trees affected and potential water bans in effect for many areas, Andersen recommends watering only those trees that you can help. How much water a home landscape needs depends upon its soil, sun and shade exposure, types of plants, irrigation system and local climate. How much water a tree requires is also dependent on its species. Applying the right amount of water, based on the local weather and the tree's actual need, is the key to using water efficiently. Water trees and lawn separately, providing what each needs specifically.


What else can be done under local water restrictions?

  • Mulch: 3-inch layer out to the drip line. (see more above)

  • Reduce or eliminate the use of high-nitrogen fertilizers. High-nitrogen fertilizers contain salts that can damage stressed tree tissues. Also, nitrogen fertilizers push new tree growth, which can exhaust tree energy when stressed.

  • Prune out only dead wood to reduce attacks by insect and disease pests. Do not remove live tree tissues until tree health improves.

  • Prevent any further stress from construction activities, lawn herbicide applications, or foot-traffic over the root zone.


Outlook: The aftereffects of drought may last three to five years, with the strongest trees surviving. Trees have developed their own mechanisms for coping with these cycles, but some trees are on the brink of survival and could go either way. "If it means the difference between keeping a tree around for your lifetime or losing it in the next five years," Andersen says, "it's worth doing something about."

Find a professional


A professional arborist can assess your landscape and work with you to determine the best course of action to care for and maintain the trees and shrubs in your landscape. Contact the Tree Care Industry Association, a public and professional resource on trees and arboriculture since 1938. TCIAhas more than 2,400 member tree care firms and affiliated companies. All member tree care companies recognize stringent safety and performance standards and are required to carry liability insurance and workers' compensation insurance, where applicable.


TCIA has the nation's only Accreditation program that helps consumers find tree care companies that have been inspected and accredited based on: adherence to industry standards for quality and safety; maintenance of trained, professional staff; and dedication to ethics and quality in business practices. An easy way to find a tree care service provider in your area is to use the "Find A Tree Care Company" program. You can use this service by calling 1-800-733-2622 or by doing a ZIP Code search on [] .