Extension Educator, Horticulture
Wet feet. A welcomed sensation while strolling along the beach or wading in a dog-cooling stream. However wet feet in winter translates into cold soggy shoes and cranky kinsman. Horticulturalists affectionately call plant roots in water logged soils as "wet feet". We can take off our shoes and dry our feet before they get too pruney, but plants are destined to live in a MAD world – Move, Adapt or Die.
Many variables go into figuring how well a plant will survive water logged soils or wet feet. A major variable is the species of plant. Some such as floodplain trees of sycamore and silver maple tolerate and even thrive in wet soils. Survivability also depends on the plant age, size and general health as well as the type of soil, how long the area is flooded, depth of the water and whether the water is flowing or stagnant.
Whether a plant will or can move, adapt or die depends a great deal on time. If the additional water occurs gradually over years, plants could move by seed or roots to higher, drier ground. If the flooding occurs gradually over many years and many plant generations, a plant species might adapt over time to better tolerate wet areas. Unfortunately our flooding events are often sudden and prolonged.
So why do plants choke or even die in water logged soils? Back in grade school you probably learned that plants need carbon dioxide from the air in order to make their food through photosynthesis. You may not remember but it's somewhere in the dusty folds of your brain that plant cells, as well as all living cells including ours, need oxygen in order to respire to use that food for energy. So plant root cells need oxygen to live. Typically they get it in the air spaces between soil particles. When soils are water logged all the air is pushed out by all the water. Cells basically drown and roots die.
Plants with root dieback may wilt during the growing season, however sometimes the symptoms of root death are not obvious. Symptoms in woody plants include leaf yellowing, red or purple leaf color, brown leaf margins, stunting, twig dieback, absence or diminished fruit yield, leaf drop and downward bending of leaf petioles. Plants stressed by too much water are also more susceptible to insect and disease attack.
Plants with water injured roots may also die or experience twig dieback later from drought stress. As soils dry, the reduced root system can't keep up with the water needs of the plant.
Woody plants that tolerate waterlogged soils include black alder, green ash, hackberry, bald cypress, redtwig dogwood, eastern larch, red maple, eastern cottonwood, swamp white oak and black tupelo.
Intermediate tolerance includes eastern arborvitae, arrowwood and American cranberry bush viburnum, white ash, basswood, Japanese barberry, river birch, black walnut, gingko, shagbark hickory, sweet gum, tuliptree and bur and pin oak.
Tree and shrubs intolerant of wet conditions include American beech; gray, paper and European white birch; eastern red cedar; cherry; crabapple; flowering dogwood; forsythia; redbud; American holly; saucer magnolia; northern red and white oak; peach; red and eastern white pine; sugar maple; blue, Norway and white spruce; serviceberry and yew.
Once plant damage occurs there isn't much we can do besides basic tender loving care such as watering plants during drought periods. However, don't be too quick to remove plants showing symptoms. If they show obvious stem rot at the soil line or don't leaf out in the spring, it's time to go plant shopping. We can't always plan for flooding but this year may be a good test of how well your plants tolerate wet soils. In regularly wet areas plan now to add plants that enjoy wet feet.