Repairing flooded lawns
Lawns can be flooded by heavy rains or overflow of streams and rivers. In early spring, before lawns begin active growth and the ground is thawing, lawn grasses can withstand several days of submersion without being seriously damaged. During the summer, however, during periods of high temperatures and sunlight, water that ponds on a lawn can cause significant damage or loss even within a few hours.
A spring flooded lawn covered in silt and debris. Remedies for this situation would include removing the silt and debris, aerating, and interseeding.
Lawn damage due to flooding
Damage to lawns from flooding can be separated into two main categories: primary damage and secondary damage. Primary damage includes such factors as water temperature and water depth. Water temperature will probably be the most important factor determining survival, with turfgrass death occurring in only a few days when water temperatures are 80 degrees F and higher. When water temperatures are lower the turf can still die, with lack of oxygen being the primary culprit. Secondary damage might be associated with sediment buildup, fungal diseases, moss and algae, and weed infestation.
Timing of repair can be difficult. The cool-season grasses that we grow in Minnesota do not establish well in the middle of the summer due to the high heat and diseases that may occur. If at all possible, we recommend waiting to seed until temperatures cool in the early fall around mid- to late-August. Fall seeded lawns will have a much better chance of a successful establishment. With that being said, recovery in the short term could be promoted by aerating your soil once it is dry and/or applying light rates of nitrogen based fertilizer.
Repair for spring flooding
For spring flooding, the most significant effect is likely to be deposit of sediment over lawn surfaces. Where silt has completely covered the lawn surface, you may want to reestablish a lawn.
- As soon as the lawn is dry underfoot (this could take several weeks), aerate it by going over it several times with a core-type aerifier. Repeat the process in early September and again the following spring.
- Overseed after aerating, or delay seeding until mid-August through mid-September. Break up aerification cores with a lawn or power rake. Sodding can be done throughout the growing season.
- Pre- and/or post-emergent herbicides may be needed to treat weed introductions from silt deposits.
Repair for ponding
Ponding occurs where there is poor drainage or depressions in the lawn. Install subsurface drainage to eliminate ponding in the future. Poor drainage can also be attributed to soil composition; it may be beneficial to have a soil test done prior to repairing the area. It is important that any soil or amendments added to fill any depressed areas are similar to the existing soil to avoid further problems.
Consider these tips to help reduce the damage and recover from flooding:
- Sandbag high risk turf areas to reduce the extent of flooding and buildup of silt.
- Remove all debris and silt from smothered turf areas as soon as possible.
- Smothered turf should be aerated to allow the exchange of oxygen and encourage new growth.
- Avoid planting perennial ryegrass, as it is generally less tolerant of flooding than other turfgrass species.
- Consider completely renovating lawns that are not easily repaired.