Missouri's Wet Springs: How Flooded Soil Affects Trees

Tree roots consume more oxygen during the growing season, making floods during that time especially damaging.  A flood in late winter or early dormancy is far less harmful than the same event in May or June. 

Missouri is seeing increased rainfall in the spring, making overly saturated soils and standing water more common. Knowing how to immediately care for trees in flooded areas, as well as long-term solutions, will help combat the negative effects of standing water. 

Why Saturated Soil Is So Harmful to Trees 

Most trees require balanced soils with air pockets that tree roots use to respire. When those pockets become waterlogged, tree roots begin to suffocate. In standing water, anaerobic conditions can develop, and toxic gases such as hydrogen sulfide can build up, further damaging roots. The longer roots are submerged, the greater the damage. 

Tree mortality rate increases when roots are exposed to standing water versus merely saturated soils. Flowing water is generally less harmful than stagnant water. 

According to the University of Minnesota Extension, upland tree species typically tolerate only 1-2 weeks of standing water over the root crown. This means that, during shorter growing seasons, floods can damage roots within days. 

Which Missouri Trees Are Most Vulnerable to Wet Springs? 

Upland trees are adapted to higher, drier, and more rugged terrain, whereas bottomland or floodplain trees are adapted to lower, wetter, and more level terrain. Upland species, like white oak, red oak, sugar maple, and flowering dogwood, are more susceptible to damage from wet springs and often don’t tolerate even brief growing-season flooding.  

Bottomland native trees like silver maples, sycamores, green ash, and cottonwoods handle wet conditions better. 

Signs Your Tree Is Stressed by Saturated Soil or Standing Water 

Symptoms may not appear until weeks, months, or even years after a flooding event. When that time comes, make sure to check for these signs of stress: 

• Yellowing leaves
• Early defoliation
• Wilted or undersized leaves
• Canopy dieback
• Peeling or discolored bark near the base
• Water sprouts along the trunk
• Recent or increased leaning or soil heaving around a tree, which indicates a soil’s loss in anchoring strength 

Pests & Diseases That Attack Flood-Stressed Trees 

Flooding doesn’t stress trees directly; it also makes them targets for pests and diseases. Stressed trees emit volatile compounds that attract boring insects and are less able to defend themselves against fungal pathogens.

Root Rot Diseases (Phytophthora, Pythium, Armillaria) 

Root rot diseases caused by molds like Phytophthora and Pythium thrive in waterlogged conditions. Oxygen starvation and flooding-induced wounding create ideal infection sites. Armillaria, also known as honey fungus, frequently colonizes flood-stressed trees. 

Roots infected by these pathogens can’t absorb water or nutrients, compounding the tree’s decline. These diseases can show similar symptoms to drought stress above ground. 

Boring Insects (Emerald Ash Borer, Bronze Birch Borer, Flatheaded Appletree Borer) 

Stressed trees emit ethanol and other volatiles that attract wood-boring beetles. The emerald ash borer (EAB), bronze birch borer, and flathead appletree borer all prefer weakened hosts. If a flood-stressed tree was borderline EAB infested, a wet spring could push it over the edge. 

Borer damage compounds flood stress. Don’t assume decline is water-related without checking for exit holes and galleries first. 

Canker Diseases (Biscogniauxia, Cytospora, Botryosphaeria) 

Canker fungi enter through wounds and weakened tissue, both of which are created by flooding. Biscogniauxia (formerly Hypoxylon) canker is especially triggered by stress. Missouri homeowners may notice peeling bark or sunken dead areas on limbs in the weeks following a saturated spring. 

Fungal Leaf Diseases (Anthracnose, Bacterial Leaf Scorch) 

Wet, cool springs create prime conditions for foliar fungal diseases like anthracnose, which affects many hardwood trees, including sycamores, oaks, and dogwoods. Bacterial leaf scorch causes symptoms similar to drought stress, and symptoms can appear more severe when trees are under stress. Anthracnose is usually not fatal on its own. Bacterial leaf scorch is a chronic disease that slowly kills trees over many years. Both diseases can compound other health issues with your tree. 

What to Do After Your Trees Have Been Flooded 

Practical post-flood tree care steps include: 

• Wait for water to recede before walking on saturated soil to avoid compaction
• Carefully remove excess sediment from around the root flare
• Remove debris that is pooled under the tree
• Break apart mulch layers to prevent matting and help the root zone dry faster
• Wait to fertilize until the tree has stabilized.

Long-Term Solutions: Drainage & Species Selection 

When it comes to post-flooding solutions, think beyond the immediate event. For a chronically poorly drained site, use French drains or swales to redirect water, select species that tolerate high water table levels (like river birch, bald cypress, sweetgum, and silver maple), and use vertical mulching to help address compaction and add soil amendments like biochar. 

Protect Your Missouri Trees This Spring With Davey 

Davey has certified arborists in offices throughout the St. Louis, MO area with the expertise needed to identify and treat trees affected by stress, pests, diseases, and more. Contact your local office today for a tree inspection.