Plant Pathology Infobytes

June 19, 1997
Soggy Soils Lead to Tree and Shrub Problems

Excessive rainfall and soggy soils have caused problems not only in vegetable gardens but in home landscapes as well, where roots of trees and shrubs are showing the effects of prolonged saturated soil conditions.

If roots of these plants are exposed to standing water for extended periods, roots often die from "anoxia," a term which means oxygen starvation. Damage occurs to trees and shrubs in obviously wet areas in the home landscape and to those along city streets and other landscape areas where soil drainage is poor.

Since damaged plants lack the ability to pick up water because of damaged root systems, one of the first symptoms of damage from soggy soils is wilting. Affected trees and shrubs may also show symptoms of nitrogen deficiency (leaf yellowing). Trees, such as dogwood and Bradford pear, tend to develop marginal leaf burn or leaves turn red or purple. Cessation of growth, twig dieback, and leaf drop are also frequently observed.

After the soil drains, plants with severely damaged roots may subsequently suffer drought stress and eventually die. For many of these plants, the only functioning roots are near the soil surface, and when dry weather follows a wet period, surface roots quickly dry out. Plants exposed to prior flooding become more susceptible to Phytophthora root rot or collar rot. Prolonged exposure to wet conditions promotes susceptibility to this disease.

What can be done to improve the health status of water-damaged trees or shrubs? Unfortunately, not much. Whatever can be done to improve surface drainage will allow soggy soils to aerate faster, thus improving chances of survival. Shallow ditching may help, but take care to keep it shallow! Remember, too much digging will lead to further root injury and intensified Phytophthora root rot problems. "Spiking" (making many small holes with a punch device) the root zone to improve aeration is also of questionable benefit for the same reason. Hold off on fertilization until the soil dries. Otherwise, this could lead to further root damage. Root drench with fungicides probably won't help much either.

The following classification of trees and shrubs according to tolerance of flooded or waterlogged soils has been compiled from several published sources.

Intolerant: American beech, Eastern red cedar, black cherry, crabapple, flowering dogwood, Siberian and winged elms, forsythia, black gum, hawthorn, several hickory species, American holly, black locust, Southern magnolia, sugar maple, mulberry, various oak species (blackjack, laurel, live, post, white, and Southern red), pecan, peach, shortleaf and Virginia pines, common privet, redbud, sassafras, tulip poplar, black walnut, and Japanese yew.

Intermediate: arborvitae, white ash, sweet bay, river birch, box elder, cottonwood, American elm, sweet gum, hackberry, pfitzer juniper, honey locust, silver maple, various oak species (pin, water and willow), osage orange, pear (including Bradford), loblolly and slash pines, and sycamore.

Tolerant: green ash, bald cypress, tupelo gum, water hickory, deciduous holly, red maple, overcup oak, and black willow.

If you have questions about home landscape problems, please check with us at the County Extension Office.


Written by the late Dr. Frank Killebrew

A black line that separates the body text from footer information