How long can trees survive flooding before injury results? As you might expect, this has become an all too frequent question when flood events occur. Fortunately for most trees, the prospect for survival and continued growth is good. Even flood-sensitive trees will escape injury if flood waters recede in seven days or less. But, if flood waters cover roots of sensitive trees for longer periods, injury symptoms such as leaf chlorosis (yellowing), downward curling of leaves, leaf drop, and branch dieback may occur. And in a few extreme cases, entire trees may die.
Trees Intolerant of Flooding
Some of the more common species used in Iowa that are flood-intolerant include:
- sugar maple,
- white oak,
- yellow buckeye,
- tulip tree,
- black walnut,
- redbud,
- linden,
- red oak, and
- most pines and spruces.
Researchers have found these species suffer severe injury or die if flood waters persist over their roots for one month or less. Sensitive trees growing alongside a swollen river may be pushed to their limit if flood waters persist. Hopefully flood conditions will last only a few days posing little danger to flood-sensitive trees.
Moderately Flood-Tolerant Trees
Moderately flood-tolerant species that have actually survived an entire growing season of flood conditions include:
- hackberry,
- hawthorn,
- osage-orange,
- boxelder,
- river birch,
- American elm, and
- sycamore.
Flood-Tolerant Trees
Species classified as being flood-tolerant, surviving as many as two growing seasons with their root systems under water include:
- silver maple,
- sweetgum,
- red maple,
- green ash,
- honeylocust,
- eastern cottonwood, and
- baldcypress.
Effects of Flooding
Flood waters will eventually recede but soils will undoubtedly remain wet for a long time. Saturated, poorly-drained soils may pose the greatest hazard for trees, particularly if waterlogged conditions persist for an extended period. If oxygen cannot penetrate to roots, trees may exhibit symptoms associated with flooding. Warm, dry weather is the only cure for this chronic and potentially deadly soil condition. Another hidden danger resulting from flooding is the deposition of sediment over tree roots. Silt and sand deposited to a depth greater than 3 inches also may impede movement of oxygen to tree roots, especially on small or newly-planted trees. When possible sediment should be removed.
Managing Flood Damaged Trees
Except in cases where flood waters persist for months or where trees have been injured by the sheer force of rushing water, most trees experiencing flood conditions should survive.
If flood- sensitive species begin to show flood damage symptoms, recovery may begin once soil oxygen levels return to a more favorable state. During this recovery period it is important that any additional stresses be eliminated.
In addition, if dead or dying branches are noticed in the tree crown, they should be removed as quickly as possible.
Beware of so-called "tree experts" recommending rescue treatments for affected trees. Fertilization is not a cure or remedy for root injury caused by flooding!
Finally, avoid planting sensitive species in flood-prone areas in the event of future flooding events.
What about Shrubs?
Shrubs will respond to flooding in a similar way to trees. Most woody shrubs will escape injury if flood waters recede in seven days or less. But, if flood waters cover roots of sensitive species for longer periods, injury symptoms such as leaf chlorosis (yellowing), downward curling of leaves, leaf drop, and branch dieback may occur. And in a few extreme cases, shrubs may die.
Some species will be more or less tolerant of the wet conditions. A list of these species can be found in this article: Which shrubs grow well in wet soils?
Managing Flood Damaged Shrubs
As with trees, except in cases where flood waters persist for months or where plants have been injured by the sheer force of rushing water, most shrubs experiencing flood conditions should survive. Take the same steps to manage shrubs as you would with trees.
More Information
- Understanding the Effects of Flooding on Trees (PDF)
- Managing Storm-Damaged Trees (PDF)
- Managing Flood Damaged Yards and Gardens
- Managing Flood Damaged Vegetable Gardens
- Managing Flood Damaged Lawns
- Managing Flood Damaged Perennials and Annuals
Photo credits: 1: Susan Vineyard/AdobeStock; 2: Cindy Haynes