Flood-damaged lawns and turf may be damaged after a flood. But most turf species will tolerate a few days of flooding without negative effects. However, turf that remains flooded for more than a few days (especially when it is hot) can rapidly decline due to a lack of oxygen and light. Substantial turf loss can be expected after 4 days of continued submersion. Other factors associated with flooding of turf include soil coverage, water contaminated with petroleum or pesticides, high water temperature, and algae scum.
How do floods pose a risk to lawns?
Lawns that are covered by floodwaters, even temporarily, may be subject to various types of damage. Most turf species will tolerate a few days of flooding without any negative effects. However, turf that remains flooded for more than a few days (especially when it is hot) can rapidly decline due to a lack of oxygen and light.
Substantial turf loss can occur after 4 days of continued submersion. Other factors associated with flooding of turf include
- Soil coverage
- Water contaminated with petroleum or pesticides
- High water temperature
- Algae scum
The most significant long-term effect of flooding is the deposit of sediment (“muck”), primarily silt and clay, over turf surfaces. This can lead to serious soil layering problems and even the death of the existing grass.
Short-term care for flooded turf
Once floodwaters have receded, pick up any debris, such as wood, glass, stones, nails, and other metal objects deposited on lawn areas. This debris could pose a safety hazard to mower operators and damage power mowers, as well as to people and pets. Remove leaves or any other material that may smother the grass.
Soil (“muck”) deposited on a lawn can sometimes be removed before drying by a combination of scooping/shoveling and washing with a jet of water using a hose-end sprayer. However, removal of soil may be impractical or impossible due to the size of the lawn area, the depth of the soil, the weight of the wet soil, and the ability to move it to another location.
Soil deposits on golf greens and other sand-based turf systems (soccer, football, or baseball fields) should be removed as quickly and thoroughly as possible to reduce the potential for silt and clay to move into the sand root zone, clogging the pores and reducing infiltration and permeability.
To reduce potential damages, use shovels, sweepers, and water to move/remove soil deposits. Aggressive core cultivation and topdressing will be needed to restore and maintain acceptable infiltration and aeration for affected turf systems
Why you should act fast after a flood
Why you should act fast after a flood
It is often not possible or practical to remove deposited soil from flooded turf while it is still wet. The drying process may take two or three weeks, perhaps longer, depending on the weather, soil, and drainage characteristics of the underlying soil and turf. Remediation at this point is largely dependent upon the depth of deposited soil.
Lawn repair with less than 1-2 inches of deposited soil
Lawns submerged for less than 4 days and covered with an inch or less of soil have a good chance of recovery. Assessment of potential lawn damage and recovery may not be possible until those areas have dried.
Checking for new shoots emerging from the soil or the emergence of new shoots from surviving plants is a good way to make an early assessment of the damage. Usually, once regrowth has begun, it will continue, although it may take several weeks before the lawn has completely filled in.
Core cultivation/aerification is one of the most important and beneficial operations conducted where soil deposits are less than an inch. When the lawn has begun to grow (green leaves begin to appear), go over the lawn 3-4 times with a core type aerifier. This will help improve overall soil structure, improve soil oxygen levels, help break up soil layering problems caused by the deposited soil and encourage recovery during the fall. The lawn should also be fertilized (using any lawn fertilizer, following label instructions for applying the correct rate) at this time (September-October).
Overseeding can also be done at the time of aerification. The aerification holes provide perfect conditions for the germination of grass seed. Lawn areas that are thin (or the entire lawn can be overseeded at this time) can be overseeded with Kentucky bluegrass or a Kentucky bluegrass/perennial ryegrass mix (tall fescue lawns should be overseeded with tall fescue seed), using a seeding rate of 5-6 pounds of seed per 1000 square feet. Rake the lawn lightly after seeding to work the seed into the aeration holes. Irrigate the lawn to maintain moist, but NOT saturated, soil conditions.
Lawn repair with greater than 2 inches of soil
Lawns covered with more than 2 inches of soil may be heavily damaged. With only a slight chance of recovery, the degree of recovery will vary with grass species and depth of soil. The greater the depth of soil, the slower the recovery and the less likely the lawn will recover.
If the lawn area is completely buried with many (3 or more) inches of soil, then the best strategy may be to re-establish a “new” lawn due to the extreme damage.
Reestablishment of a "new" lawn over a flood-damaged lawn
There are two ways of dealing with the deposited soil to reduce the future potential for soil layering. One is to remove as much of the soil as possible, down to the original lawn surface. Understanding that this may be difficult or impractical, the deposited soil may be left on the lawn and rototilled into the lawn as deeply and thoroughly as possible. This, in essence, will create a “new” lawn root zone that is a mix of the deposited soil and the underlying lawn and its soil. The goal is to eliminate, as much as possible, the formation of layers in the “new” lawn root zone by thoroughly mixing the original lawn’s soil, the layer of the original, dead lawn, and the flood-deposited soil.
After leveling and firming the “new” lawn soil, it can be sodded or seeded as any new lawn would be established. Cool-season grasses can be seeded anytime between Aug. 20 and Sept. 30 (buffalo grass should be seeded in April/May). Sod can also be used to provide an instant lawn. Do not sod over existing dead or buried vegetation. The old dead layer of lawn grass must be thoroughly tilled into the soil before laying new sod.
Author and Publication Date
By T. Koski.* (9/13). Revised (10/21).
Tony Koski, Extension Turf Specialist, Department of Horticulture and Landscape Architecture, Colorado State University.
Disclaimer
Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. CSU Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.
