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By Gary L. Wade
University of Georgia
Stress in our own lives weakens us and makes us more susceptible
to illness. And when environmental problems stress plants, they
become vulnerable to diseases and pests.
We can walk away from our stress or can take medicine to relieve
it. Plants, though, have to cope until someone changes their
environment or moves them to a better place.
To manage stress in the landscape, pay close attention to the
site. Select plants that are adapted to it. Change it to better
satisfy the plants’ requirements. Or apply cultural practices
that reduce stress.
Look beyond symptoms
Solve problems by recognizing that the symptoms you see may be
secondary. That insect or disease damage, leaf scorching or
nutrient deficiency is likely caused by other stresses.
For instance, your azaleas are in an extremely alkaline soil, and
you spray them with liquid iron to correct an iron deficiency
symptom. It’s a short-term solution to a long-term problem.
A good long-term solution? Remove the azaleas to a better site
and plant something that’s more tolerant of high soil pH. Or
remove the alkaline soil and replace it with acidic soil. Or
apply acid-forming fertilizers.
Control what you can
We can’t control stresses such as ice storms, freezes, floods or
drought. But we can help prevent them from damaging plants. First
consider the weather catastrophes most likely to happen. Then put
sensitive plants where they’re less prone to injury.
For instance, put the plants sensitive to moisture stress on
raised beds. Place drought-prone plants at lower sites to take
advantage of natural drainage.
Some plants such as Heller holly and dwarf Japanese garden
juniper can’t tolerate extreme fluctuations in soil moisture.
They’ll be stressed if the soil goes back and forth from very wet
to very dry.
Careful placement
Severe winter freezes typically blow from the northwest to the
southeast. So put plants that are sensitive to the cold on the
south and southeast side of a building or windbreak. That will
shelter them from Arctic blasts.
Afternoon shade is critical, too, to ornamentals such as azaleas,
dogwoods, redbuds and hydrangeas. Put them on the east side of a
building or other source of shade from afternoon sun.
The No. 1 environmental stress in Georgia landscapes is poor soil
drainage. The roots of plants growing in wet soils or soils with
a high water table literally suffocate and die.
Wet feet
Often just enough roots to sustain the plant will grow just
beneath the surface to get much-needed oxygen. A short time of
drought, a mild freeze or even fertilizing the plant can damage
the remaining surface roots and kill the plants.
A simple perk test will help avoid wet-feet stress. Just dig a
hole 2 to 3 feet deep in the native soil and fill it with water.
If more than one-third of the water is still in the hole after 24
hours, improve the drainage before you plant. You can subsoil to
break up a hardpan layer, plant on a 12- to 24-inch raised bed or
put in drainage pipe.
The right plant
Another excellent way to avoid long-term stress is just to choose
the right plant for the site. You don’t have to be a walking
encyclopedia of plants. But you do need a good reference book.
One good one is “The National Arboretum Book of Outstanding
Garden Plants,” by Jacqueline Heriteau. It lists plants adapted
to a range of sites.
When you select plants, though, never decide on one criterion
alone. Red-tip Photinia, for instance, is exceptionally
drought-tolerant. But it’s extremely susceptible to a leaf spot
disease that defoliates it in stressful situations.
A healthy plant is a happy plant. They may not have emotions as
we do, but plants waste no time showing us they’re stressed. It’s
our job to remedy these stresses so the plants can thrive.
(Gary Wade is an Extension Service horticulturist with the
University of Georgia College of Agricultural and Environmental
Sciences.)
