This summer has been rough. Day after day the heat has
topped 95 degrees. Little to no
rain has fallen for three straight weeks. And the combination
has led to serious, and
sometimes fatal, plant stress in Georgia landscapes.

Some of the plants now showing major heat and drought stress
include dogwood, Japanese
maple, oakleaf hydrangea, fothergilla and azalea.

Heat/Drought Stress
Symptoms

Symptoms range from wilting and pale yellow color to
marginal leaf scorching, leaf
cupping and defoliation. Trees and shrubs planted in the past
year and those with other
stresses (root damage from construction, for instance) are
the most seriously affected.

Annuals in nonirrigated areas are a struggle to maintain.
They fail to provide an
effective color display when they wilt day after day.

In some counties, restrictions on outdoor water use and
irrigation bans make matters
worse.

Drought stress is often compounded by an increase in insect
and disease problems.
Powdery mildew, ambrosia beetles and spider mites are three
common predators of stressed
plants.

A Matter of
Balance

Droughts stress plants when the foliage demands more water
than the roots can supply.
The stress usually results from roots’ dehydrating and dying in
extremely dry soils.

Sometimes one part of the root is affected before another
and the plant discards a
branch here and there to compensate proportionally for the
volume of roots lost.

The plant walls off the branch from the remaining live
limbs. It shuts down production
in that branch in an effort to survive.

On the other hand, sudden death syndrome, when an entire
tree or shrub dies suddenly,
is a most disappointing root-death symptom. It’s particularly
disheartening if the plant
is an irreplaceable, 100-year-old oak.

Sudden Death

Sudden death may come days, weeks or even months after the
imposed stress. The plant
appears to survive, even though the root system is dead, by
drawing on water and
carbohydrates stored in the roots. Then it dies suddenly when
the reserves are depleted.

Sudden death in spring following a drought the season before
is one of the hardest
environmental injuries to explain.

How do you help plants cope with heat and drought stress? Do
everything possible to
conserve soil moisture and prevent root injury or death.

Mulch Conserves
Moisture

Mulching is one of the best ways to conserve moisture in the
soil. Fine-textured
mulches such as pine straw, pine-bark mininuggets or shredded
wood mulch hold moisture in
the soil better than coarse-textured mulches.

Spread mulch not just under the canopy, but as far beyond
the canopy as you can, since
roots extend two to three times the canopy spread.

Pruning Can
Help

Summer pruning may be necessary to reduce the leaves’ demand
on the roots. If a tree or
shrub wilts or begins to show leaf scorching or other stress
symptoms, thin the canopy by
one-third to one-half, depending on the severity of the
stress.

With selective thinning cuts, you can reduce the size of the
canopy without destroying
the plant’s shape.

Annuals and herbaceous perennials showing moisture stress
can be cut back to within 6
inches of the ground. Most will return with vigor, assuming
they get some moisture to
sustain what growth is left.

Do No Harm

During periods of heat and drought stress, avoid any further
stresses on the plants’
roots.

Fertilizing a drought-stressed plant is one of the worse
things you can do. Chemically,
fertilizers are salts. They will pull water from the roots,
dehydrating them further.

Avoid disturbing the roots by digging, too, or suffocating
them by placing soil over
them.

When the weather breaks, regular rains return and cooler
fall temperatures arrive,
apply a phosphorus-based fertilizer, such as Superphosphate, at
one-half pound per 100
square feet around stressed trees and shrubs. That will help
them rebuild their roots
during the fall and winter while the top is dormant.