Caring for Flooded Lawns – Warm Season Grasses

— Written By N.C. Cooperative Extension

Now that the storm has passed, it’s time to begin looking at the impacts on your turf. Because we are going into the dormant season for turf, you will not really know the impact of the flooding on your lawn until next spring. As the turf greens up next spring watch your lawn to see if recovery is spotty or generally thin.

Debris:  Pick up any debris, such as wood, glass, stones, nails and other metal objects deposited on lawn areas. This debris is a safety hazard and can damage power mowers. Remove leaves or any other material which would smother grass.

Silt Defined:  In some areas receding water may leave a residue of soil on your lawn. The residue is called silt. As the river or flood waters move, they pick up particles of soil that are typically in size between clay and sand. As the water begins to recede, the silt settles onto the ground and can be left on the flooded area. This can result in damage to the landscape, but in some cases silt will improve the soil if not in too large amounts.

Silted Lawns—1 Inch or Less:  Lawns submerged for less than 4 days and covered with an inch or less of silt have a good chance of recovery. To assist recovery:

  • If water use is unrestricted in your area, wash as much silt as possible from the lawn using a garden hose.
  • To encourage root development, keep the remaining silt crust broken throughout the growing season, or until grass has become well-established. Use a steel tooth garden rake, a mechanical aerator, or spiking equipment to break up the silt crust.
  • Have a soil sample tested as soon as possible to determine lime, phosphorous and potassium requirements of soil. Follow the recommendations given with test report.

Silted Lawns—More Than 1 Inch:  Lawns covered with more than 1 inch of silt may be heavily damaged, with only a slight chance of recovery. Degree of recovery will vary with grass species and depth of silt. Re-establish the lawn as follows:

  • Remove as much silt as possible, especially if silt accumulation exceeds 3 inches.
  • If silt is less than 3 inches, or has been removed to this depth, till the area, making sure the silt is mixed thoroughly and uniformly through the top 4 inches of the original soil.
  • Take a soil sample of the new soil mixture after silt has been mixed in. Have the mixture tested to determine lime, phosphate and potash requirements. Even if you are not able to till in the silt that has been left on your turf, be sure to take a soil sample and follow the recommendations.
  • It is best to retill after applying lime and fertilizer according to soil test recommendations.
  • Reseed or vegetatively replant the area as you would to establish a new lawn. Warm season grasses are typically planted by sod, seed or sprigs. Because of the time of year, seed bare areas with common rye grass. This will hold the soil in place until the appropriate time to plant your preferred type of turf.
  • Centipede and Zoysia may be seeded, sprigged or sod laid from March to July, Bermudagrass and St. Augustine from April to July. Complete information on turf maintenance can be found on-line at: https://content.ces.ncsu.edu/carolina-lawns

Flooded Lawns:  Degree of injury will depend on duration of submergence, water depth, temperature, grass species, light intensity and the condition of grass prior to flooding. Grass will survive much longer at water temperatures below 60 degrees F than at higher water temperature.

Most grasses will survive 4 to 6 days’ submergence at normal summer temperatures. Aerate and lightly fertilize flooded areas as soon as possible after the water recedes. Areas submerged longer than 4 to 6 days may not survive and will require complete reestablishment as noted above.

Loss of Topsoil—Eroded Areas

  • Where topsoil has been greatly eroded, replace it to a depth of 4 to 6 inches late in the growing season.
  • If topsoil is unavailable or too expensive, improve existing soil by adding organic matter such as peat, rotted sawdust, manure or other materials. Apply these materials at a rate of 3 cubic yards per 1000 square feet of lawn area, and work materials into the top 4 inches of subsoil. A temporary lawn, established immediately and later worked into the subsoil, can also be a source of organic matter.

Establishing Temporary Lawns

  • Where lawns must be completely re-established and immediate cover is needed, scratch the soil surface with a hand rake or similar tillage tool.
  • Seed common ryegrass at a rate of 4 to 5 pounds per 1000 square feet. In our area, ryegrass will die out when summer arrives.

Oil and Chemical Spills:  Soils may have been saturated with oil, herbicides, or other toxic material. Petroleum will eventually decompose, but nothing can be done in the meantime to counteract its harmful effects. On large areas, bury oil deposits by deep plowing. On small areas, remove petroleum-soaked soil to a depth of 6 inches, and replace with new topsoil. Reseed or vegetatively plant at the appropriate time.

Turf Diseases:   Turf diseases may be prevalent on surviving turf areas. Contact your County Extension Agent for advice on fungicide application.

Weeds:  Flood water may carry and spread weed seeds. However, weed control should not be a primary concern since a weed cover is better than no cover and will even help dry out soil. Weeds can be controlled best with chemicals in the fall or spring. Contact your County Extension Agent for proper chemical controls.

For more information, contact Shannon Newton, Area Horticulture Extension Agent, by phone at 910-875-3461 or by e-mail at Shannon_Newton@ncsu.edu.

Information adapted from “Caring for Flooded Lawns,” University of Florida

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