Repairing flooded lawns
What can you do when your lawn is flooded—either by heavy rains or the outflow of streams or rivers? In the early spring before lawns begin active growth and the ground is still thawing, lawn grasses can withstand several days of being submerged without suffering serious damage. However, during summertime, periods of high temperatures and high light conditions, any water that ponds on a lawn surface can cause significant damage or loss even within a few hours. Ponding occurs in areas of poor drainage or results from water being left behind in valleys and depressions when floodwaters recede. Noting these locations and correcting any surface or subsurface drainage problems is prudent for creating a healthy lawn environment for the future. Areas where the grass has been completely lost will need to be restored through reseeding or resodding.
Spring flooded lawn areas, where the water has risen and then receded rapidly, are not likely to experience extensive injury. The more significant effect of flooding is likely to be the deposit of sediment, primarily silt, over lawn surfaces. This can lead to serious soil layering problems and even death of existing grass if deposits are deep enough.
Once floodwaters recede, don't start working in the area immediately. Wait until it isn't soggy under foot. The drying process may take several weeks. Damage assessment and recovery of the existing lawn may not be possible for a few weeks. Once the lawn has dried, thoroughly aerify it by going over it 3 times with a core type aerifier. Repeat the process in early September and again the following spring.
Aerification is especially important where silt is deposited over the lawn. If silt depth is barely detectable over the surface, thorough aerification may be sufficient. The lawn may be completely covered with silt and the grass plants barely visible or completely buried. REMOVING SILT IS WORK and can be very damaging to the existing grass plants. Therefore, you may want to establish a new lawn.
Perform necessary overseeding at the time of aerification or delay seeding until mid-August through mid-September. To prepare a smooth seed bed, break up the aerification cores with a lawn rake or power rake. Sodding can be done successfully throughout the growing season.
Another problem with silt deposits is the introduction of potentially new and different weeds to the lawn. Pre-and/or post-emergence herbicides may be used where appropriate.
Remember, if you are dealing with a flooded lawn, wait until the soil is sufficiently dry.