Issue 6, June 5, 2017

Waterlogged Plants

It's no secret that much of Illinois has received excessive spring rains, which has resulted in waterlogged soils and flooding. It is important to understand what is happening to plants growing in these conditions and what to expect later. I look at this as "a wait-and-see situation." Many herbaceous plants are experiencing injury symptoms now. Visible injury symptoms on trees and shrubs may not occur for a year or more.

Injury symptoms, which vary according to several factors, include slower shoot and root growth, leaf yellowing, leaf twisting, leaf drop, root death, increased susceptibility to attack by insects and disease, absence of fruiting, and death.

The main reason injury occurs is related to oxygen availability in the soil. In flooded or waterlogged soils, roots are robbed of oxygen. When roots can't "breathe," they can't provide necessary nutrients to upper plant parts.

Although survival is directly related to a species tolerance of waterlogged soils, other factors are important including the soil type; the time, duration, and depth of the water; the state of the floodwater; and the age and size of woody plants. Plants that are native to wetter habitats typically do better in wet situations.

Tolerant species such as bald cypress, littleleaf linden, red twig dogwood, mulberry, silver maple, and willow can live on sites in which the soil is saturated for indefinite periods during the growing season.

Moderately tolerant species such as green ash, hawthorns, honey locust, pin oak, red maple, river birch, sweetgum, and sycamore can stand soggy 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, crabapples, eastern hemlock, flowering dogwood, paper birch, pines, redbud, spruces, sugar maple, tuliptree, white oak, and yews die if subjected to short periods of 1 or 2 weeks of soil saturation during the growing season.

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. (Rhonda Ferree)

Rhonda Ferree

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