Flooding and waterlogged soil: what extension services describe for trees

This page describes what the named extension services and the Missouri Botanical Garden say. It does not diagnose a tree, say whether any flooded tree is safe or unsafe, or tell anyone to treat, replace or remove one. It covers flooding and soil that stays saturated, whether from a river, poor drainage or too much irrigation, because the sources describe the same root problem in each case.

What the sources say happens to the roots

The Missouri Botanical Garden says heavy, poorly drained soils are prone to waterlogging, and that roots in waterlogged soil may die because they cannot take up the oxygen they need. It says the longer the air is cut off, the greater the root damage, and that dying roots decay and stop supplying water and nutrients. Utah State University Extension (Overwatering, Ornamental Pest Guide) says saturated soil displaces air and starves roots of oxygen, killing roots and weakening water uptake, and that tree death can occur where standing water persists. Iowa State University Extension and Outreach (Yard and Garden, Jeffery Iles, reviewed June 2024) says saturated, poorly drained soils may pose the greatest hazard to trees, especially if waterlogging lasts, and that silt or sand deposited deeper than 3 inches over roots can also block oxygen, especially on small or newly planted trees.

What it looks like

Iowa State lists leaf yellowing, downward curling of leaves, leaf drop and branch dieback. Its question-and-answer entry (last updated February 24, 2022) adds reduced leaf size and shoot growth, epicormic sprouting along the stem or trunk, early fall color and crown dieback, and says large seed crops can follow on stressed trees in the next growing season. It says the symptoms may progress to decline and death, reappear for several years and then fade, or subside after a single growing season. Utah State lists canopy dieback, yellowing, dead tissue, marginal scorch, wilting and leaf loss. Missouri describes stunted, slow growth with yellowing leaves, leaf scorch or burn, water-soaked spots and blisters on stems and leaves, and a rotting plant crown.

How long the sources say trees tolerate flooding

Iowa State says flooding during the growing season is typically more harmful than flooding while trees are dormant, and that the longer the exposure, the greater the potential for injury. It says most trees escape injury if floodwater recedes within seven days, and sorts species into three groups. It lists sugar maple, white oak, yellow buckeye, tulip tree, black walnut, redbud, linden, red oak and most pines and spruces as flood-intolerant, reporting researchers found severe injury or death if water stays over their roots for one month or less. It lists hackberry, hawthorn, osage-orange, boxelder, river birch, American elm and sycamore as moderately tolerant, having survived a full growing season of flooding. It lists silver maple, sweetgum, red maple, green ash, honeylocust, eastern cottonwood and baldcypress as tolerant, surviving as many as two growing seasons with roots under water. It says that apart from cases where flooding lasts months or the force of the water injures trees, most trees experiencing flood conditions should survive.

Look-alikes and linked problems

Missouri says damage from waterlogging is frequently misdiagnosed as pest damage, and that one clue it gives is that pests rarely cause roots to gather near the soil surface. It says plants stressed by waterlogging can become unusually open to some fungal pathogens, naming Phytophthora root rot as most common in soils that are periodically waterlogged, and that soil kept too long without oxygen usually smells sour or rotten. Utah State says overwatering can cause as much stress as severe drought, and Missouri says drought symptoms can resemble overwatering: see the page on drought stress. Missouri lists leaf scorch as a possible symptom of overwatering, and the page on leaf scorch sets out the other causes the sources name. Colorado State University Extension lists overly wet or dry soil among the conditions that bring on iron chlorosis.

The other pages in this group are listed on the weather, soil and chemical damage page. For how roots use oxygen, see how a tree works.

Flooding and waterlogged soil: what extension services describe for trees

What the sources say happens to the roots

What it looks like

How long the sources say trees tolerate flooding

Look-alikes and linked problems

Sources