How To Protect Vulnerable Trees
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
- Rabbits and Deer
- Wisconsin Winters
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.
Close Stomata: The first stratagem is to close the microscopic pores, stomates
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.
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.
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
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.
There are quite a few products available to help you sustain sufficient soil mosture for your
trees during times of heat stress making your watering job a LOT easier!
Tree Watering Bag
Quick-Fill Deep-Soak Watering Kit
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
Water on overcast days, early in the morning or in the evening. Evaporation is slower during
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
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