Heat, Drought Take Toll on Landscape Plants
Temperatures in the high 90s and several weeks without rain can lead to serious, sometimes fatal, conditions for landscape plants.
The plants that are among the first to show major heat and drought stress include dogwood, Japanese maple, oakleaf hydrangea, fothergilla and azalea.
Heat stress 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.
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.
Plants become stressed when their foliage demands more water than their roots can supply. The stress usually results from roots dehydrating and dying in extremely dry soils.
How do you help plants cope with heat and drought stress? University of Georgia horticulturists say do everything possible to conserve soil moisture and prevent root injury or death.
Mulching is one of the best ways to conserve soil moisture. 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. Keep in mind, roots extend two to three times the canopy spread.
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.
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, further dehydrating them.
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. This will help them rebuild their roots during the fall and winter while the top is dormant.