Most of Illinois has experienced excessive rains, resulting in waterlogged soils and flooding. It is important to understand what happens to plants growing in these conditions and what to expect later. It is a wait-and-see situation. Many herbaceous plants are showing injury symptoms now. Visible injury symptoms on trees and shrubs may not occur for a year or more.
Injury Symptoms. Injury symptoms, which vary according to several factors, include decreased growth of shoots and roots, decreased transpiration rate, leaf chlorosis (yellowing), leaf epinasty (twisting), leaf abscission (drop), root death, increased susceptibility to attack by predators and pathogens, absence of fruiting, and death.
The main reason for injury relates to oxygen depletion in flooded or waterlogged soils. As oxygen slowly diffuses and reduces in concentration to a few percent or zero, aerobic root respiration, root growth, transpiration, and translocation all decrease or stop.
Factors Influencing Survival. Although survival is directly related to a speciesí tolerance of waterlogged soils, other important factors include soil type; time, duration, and depth of flooding; the state of the floodwater; and the age and size of woody plants.
Tolerant species such as bald cypress, littleleaf, linden, redtwig dogwood, mulberry, silver maple, and willow can live on saturated sites for indefinite periods during the growing season.
Moderately tolerant species such as green ash, hawthorn, honeylocust, pin oak, red maple, river birch, sweetgum, and sycamore can stand saturated soil for a few weeks to several months during the growing season but die if waterlogging persists or reoccurs for several consecutive years.
Weakly tolerant species such as American holly, balsam fir, black walnut, bur oak, catalpa, hackberry, Douglas-fir, eastern cottonwood, and red oak can stand relatively short periods of soil saturation (a few days to a few weeks) during the growing season but die if waterlogging persists for longer periods.
Intolerant species such as American beech, black locust, crabapple, eastern hemlock, flowering dogwood, paper birch, pine, redbud, spruce, sugar maple, tuliptree, white oak, and yew die if subjected to short periods of one or two weeks of soil saturation during the growing season.
What To Do Now. Unfortunately, little can be done to prevent damage to plants growing in waterlogged soils. If a woody plant shows injury symptoms, such as leaf drop, do not immediately replace it. Some plants will show initial injury symptoms and then recover. Many woody and herbaceous plants, including turf areas, will not recover. Be patient. Whether your plants are simply waterlogged or actually growing in flood areas, it will take a while to see the full extent of plant damage.