Any homeowner who has suffered from flood waters in the yard will find getting the lawn back can take some time. Several factors impact the amount of damage and the recovery, including what kind of grass, what season, and how long the area stayed flooded.

Temperature and tolerance

Water temperature controls how long grasses can stay submerged and survive, according to Dr. Bruce Branham, University of Illinois professor and faculty Extension specialist. “Spring flooding with cold water often results in minimal damage. Summer flooding with warm water can cause rapid turf death if submerged more than a day or two. Turf grasses vary significantly in their tolerance to flooding. Fine fescues have poor submersion tolerance and can be killed in as little as a day of submersion under warm water. On the other hand, creeping bentgrass has excellent submersion tolerance and can tolerate several days of flooding. Kentucky bluegrass has medium submersion tolerance while perennial ryegrass has fair tolerance to submersion injury.” (Beard, 1973)

Tips and timing

If the water came and went, but left the lawn covered with silt, the silt should be removed as soon as possible with water from a hose. This will allow the grass blades to start producing energy to aid in recovery. The floodwater filled all the available pore spaces in the soil displacing any soil oxygen. All plants need that soil oxygen to actively absorb nutrition from the soil. In areas where water has stood for many days, the grass plants are not likely to have survived and more recovery or repair will be needed.

Table 1 Timetable for seeding (can vary by 2 weeks or more)

Adapted from Master Gardener Manual University of Illinois

Seeding at the proper time allows grass seed to germinate, grow, and be mowed several times before the growing season ends. “Seeding can be done any time of year, but the best chance of success occurs when seed is planted in the late summer/early fall timings shown in Table 1,” according to Branham.

Spreaders, seeders, and species

Seeding options include a traditional broadcast seeding using a drop or centrifugal spreader or using a rental “slit seeder” that cuts through the dead grass and thatch layer and places the seed directly in the soil at the proper depth. For areas up to 200 square feet, you can get good seed-soil contact by buying a small amount of topsoil and lightly covering the seed that was broadcast over the area. This approach is practical for relatively small areas, but for larger areas, a slit seeder will give you the best results. If using a slit seeder, be sure to go in two directions to ensure a better stand of grass in the coming weeks.

Grass seed is sold a couple of ways, and what you choose depends on your needs. Blends combine several grasses of the same species (i.e. all cultivars of Kentucky bluegrass) or as a mix combining different species (i.e. Kentucky bluegrass and perennial ryegrasses). Your choice depends on the quality of lawn you want to have or maintain and the sun-shade pattern. In older lawn settings, a mixture may be preferred since over time a single species blend naturally becomes a mixed lawn. Perennial ryegrasses can germinate in as little as 3 to 5 days while bluegrasses can take 10 to 14 days. If the lawn has been growing in shade, consider fine fescues being much more shade tolerant than bluegrasses as part of the mix.

If only a portion of the lawn has been damaged, you should identify what species are present and match the seed you purchase to the species in the lawn. If the lawn is mostly Kentucky bluegrass, then purchase a Kentucky bluegrass blend. While bluegrass, ryegrasses, and fescues mix well and generally don’t appear patchy. Branham also cautioned, “beware of very inexpensive seed, as it often contains annual ryegrass. Annual ryegrass germinates very rapidly, usually in 3 to 4 days, but grows upright quickly, is a pale green in color, and will not blend in with other grasses in the lawn.”

Weeds and their seeds

As the water recedes, many kinds of weeds can and will show up from the seeds left behind from flooding. Some will germinate but not tolerate mowing and naturally die as the lawn is mowed. However, there will be the opportunity for lots of weed seed germination the following spring –over 90 percent of weeds are spring germinators – and some of them will have the same fate and not tolerate of being mowed. Annual weeds that germinate each spring are killed in the fall by frost, but to prevent future populations, do not let them self-seed. If perennial weeds establish themselves and survive being mowed, then weed control treatments will be needed to remove them from the lawn. Whatever direction taken, focus on establishing the lawn, weeds can be managed later. Satisfactory recovery of the home lawn can take two years.

About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.

Beard, J. B. (1973). Turfgrass: Science and culture. Englewood Cliffs, NJ: Prentice-Hall.