NC State Turf Alert – Submerged Turfgrass
The following article was prepared by NCSU Extension Turf Specialist, Dr. Grady Miller:
The more severe turf damage is typically from the storm surge pounding turf with salty water. In many cases once the water subsides and the ground begin to dry, the turf may die from salt injury. If not near the coast, salt damage is less of an issue. But the high rainfall rate and the fact that the ground was already saturated from previous storms means widespread flooding in many coastal and inland areas.
Turf injury from submersion can be variable depending on the conditions. These include turfgrass species, water temperature, duration of submergence, and depth of submergence. Observations have indicated that turfgrass can withstand submersion for up to 60 days when water temperatures are below 50 F. On the other hand, turf can be killed in one day when water temperatures are in the high 80s F or higher. Temperatures were between these for this storm. Submersion injury also increases when the entire plant is submerged. If the plant is submerged for more than a few days under water that is cloudy with silt, clay and debris, it is more damaging than if the water is clear. In addition, flood waters may contain toxic contaminants such as salts or petroleum. These may cause longer-term problems because the contaminant may linger in the soil, impeding regrowth. Even low levels of salts can indirectly affect plants by reducing water uptake or by causing an imbalance of plant nutrients. And while it may seem minor, the lack of oxygen to the roots brought on by saturated soils may cause turf loss.
Understanding the cause of your damage helps in developing a plan to renovate the turf. If the floodwaters deposited silts and clays on the surface, these should be removed with shoveling, hosing, power washing, etc. In some cases debris and soil material can be blown off the surface with a blower. The air flow from the blower can also hasten the soil drying process. If the grass does not begin to green up by the time the soil begins to dry out, it may be a sign that the turf is dead or that it is so severely set back that regrowth is going to be very slow. Given enough time, bermudagrass will grow back from almost any flooding damage. But if the damage is more than just a thin turf, and time is an issue, it may be better to start over completely.
If the damage is not too severe, begin aerification once the area can support a lightweight aerifier or tractor-mounted aerifier. Not only will this alleviate compaction, but it will help break up the soil layers and get more oxygen into the rootzone. If the flooding was associated with a salt-water storm surge, then leaching the saltwater out of the rootzone may be necessary. Additional rainfall from the storm may act as a “self-flush” to the rootzone. In the absence of rainfall, the irrigation system may be used to dilute and move the salts below the rootzone.
Once the water has subsided and the rootzone begins to dry, initiate a normal grow-in fertilization and irrigation program appropriate for your grass and soil conditions. Consider the need to alter your herbicide program. Note that the moving floodwaters may have replenished your weed seed bank.
Long-term problems will also reflect the type of initial storm damage. With rainfall and irrigation, salt damage should be fairly short-term. If topsoil was eroded and replaced before renovation, there may be some long-term variation in turf growth and color due to differences in soil. Also, any silt and clay deposits that were not removed may result in long-term visual and performance differences. Regular aerification and topdressing should address these problems over time.