Trees can’t escape the extreme heat. But they do have some impressive coping mechanisms.

How To Protect Vulnerable Trees and Shrubs

Part 1 of a 3-part series

You have spent a chunk of change as well as your time in effort in establishing trees. They are leafing out and adding character and color and perhaps a little shade in your yard. What are you doing to prevent your investment from:

  Heat Stress

How Trees Cope With Heat

Trees are, among other things, great columns of water, drawing moisture from the soil and exhaling it through the leaves. It has been estimated that a single apple orchard can lift 16 tons of water a day.

This is not to say that trees are not stressed by this heat or have not had to adopt mechanisms to cope with it.

As temperatures climb into triple digits and humidity raises the heat index to insane levels, trees adopt two basic and related strategies.

Leaf stomata diagram

Closed Stomata: The first stratagem is to close the microscopic pores, stomatas, found mostly on the undersides of the leaves. This shuts down transpiration and the gaseous exchanges needed for photosynthesis , in which the tree takes in carbon dioxide and releases water and oxygen.

Wilted tree leaves Wilt: The second stratagem is to wilt. Prolonged wilting in drought-stressed plants, especially young ones, can be deadly, but temporary wilting on established trees and shrubs is a defense mechanism and can occur even if soil moisture is adequate.

By folding its leaves, the plant reduces its foliar surface area to sunlight and reduces the evaporative effects of the wind.

  Strategies To Reduce Heat Stress


Wilting and curling leaves will appear on drought stressed deciduous trees. Leaf edges will eventually turn brown and crispy and may drop prematurely. Evergreen needles will begin to turn brown at the tips. As the drought continues the entire needle will turn brown.


Generally, the trees most at risk are those that are newly planted or transplanted. The root system of these plants is underdeveloped or has been damaged. Trees that are growing in a restricted area should also be of greater concern. This will include tree planted in containers, the grass strip between the street and sidewalk and trees grown adjacent to your house or driveway. Drought-sensitive plants like birches, beeches, dogwoods, Japanese maples and magnolias should also be given priority during drought conditions.


It is best to begin good watering practices before the tree succumbs to drought stress. Trees need approximately one inch of water per week. If Mother Nature is not supplying it then you should.

It is best for the tree if the required water is applied all at one time to the soil, slowly and deeply. This can be accomplished by using irrigation bags on newly planted or small trees. Trees in a restricted area are best watered with a slow dripping hose placed at the base of the tree and moved frequently for even distribution. For larger trees, a soaker hose laid in a spiral pattern, radiating from the tree trunk out to the drip line, works well.

  Helpful Suggestions On Tree Heat Stress

Tree Watering Systems for Heat Stress

There are quite a few products available to help you sustain sufficient soil moisture for your trees during times of heat stress making your watering job a LOT easier!

Soaker Hose
Tree Watering Bag
Quick-Fill Deep-Soak Watering Kit
Watering Timers
Root Feeders


Always water the soil and not the leaves or needles of the tree.
When watering, remember that trees absorb water through their roots, most of which are in the upper 1 to 2 feet of soil.
The goal is to keep the trees' roots moist but not wet — constantly saturated conditions can damage roots.
2 – 4 inches of mulch placed over the soil, under the tree, from the trunk to just beyond the drip line, will help to conserve soil moisture. Be certain not to mound mulch against the tree trunk.
Water on overcast days, early in the morning or in the evening. Evaporation is slower during these times.
Prune the canopy of the tree to reduce excess foliage, weak branches, and diseased plant material. If tree crowns are very dense, light thinning will help reduce demands for water and nutrients.
Fertilizer can injure tree roots during times of limited soil moisture. Avoid using fertilizer during drought conditions

More Gardening Tips:

 How To Use Coffee Grounds In The Garden
 How To Use Eggshells In The Garden
 Best Practices For Perennial Plant Fertilization
 How To Use Rooting Hormones
 Spring Pruning Basics

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