Pool water can kill grass, a common concern for homeowners. The extent of the damage depends entirely on the volume of water and the concentration of chemicals it contains. Small, daily splashes are usually negligible, yet a large spill or improper draining can quickly create dead, brown patches. Understanding the specific composition of the water and how it interacts with the grass and soil is the first step in protecting your turf.
The Primary Culprits in Pool Water
The primary agents responsible for turf damage are the sanitizers and pH adjusters used to maintain water quality. Chlorine is a powerful disinfectant that is toxic to plant life at high concentrations. While the ideal range for pool chlorine is generally low (1.0 to 3.0 ppm), a pool that has just been “shocked” can have a much higher, temporary concentration that is highly destructive. Even in saltwater pools, the system generates chlorine, but the main threat to grass comes from the high salinity.
Pool water also contains chemical modifiers used to keep the pH balanced, typically between 7.4 and 7.6. Grass thrives in a slightly more acidic soil environment, ideally between pH 6.0 and 7.0. Introducing a large amount of pool water with an extreme pH instantly stresses the root system. This rapid change in soil chemistry is a significant factor in localized grass death.
Mechanisms of Grass Damage
The chemicals in pool water harm grass through three distinct physiological processes. High concentrations of chlorine cause a direct chemical burn, which quickly denatures the proteins and tissues in the grass blades and roots. This immediate cellular toxicity results in the rapid browning and death of the plant material contacted by the spill.
For saltwater pools, the primary mechanism of damage is osmotic stress. Salt in the soil solution creates an imbalance that draws water out of the root cells toward the saltier environment. This effectively dehydrates the grass, leading to wilting, discoloration, and eventual death.
Extreme pH levels also damage grass by inducing nutrient lockout. When soil pH deviates significantly from the optimal 6.0 to 7.0 range, certain essential nutrients become chemically unavailable for the grass roots to absorb. Highly alkaline water can reduce the solubility of micronutrients like iron, causing deficiencies. Conversely, very acidic water can increase the availability of elements like aluminum to toxic levels, disrupting normal root function.
Saving the Lawn After Exposure
Immediate Dilution
A large pool water spill requires immediate action focused on dilution and remediation. The first and most important step is to flush the affected area heavily with fresh, clean water from a hose or sprinkler for at least 15 to 30 minutes. This process aims to dilute the chemical concentration in the soil and wash it away from the shallow root zone before permanent damage occurs. This is the most practical initial response for both chlorine and salt-based spills.
Neutralizing Chlorine
For large spills involving highly chlorinated water, applying a chlorine-neutralizing agent like sodium thiosulfate can speed up the detoxification process. Sodium thiosulfate quickly converts active chlorine into harmless chloride ions. For a severe, concentrated spill, a granular application of this neutralizer can minimize root burn.
Treating Salt Damage
If the damage is caused by high salinity from a saltwater pool, remediation requires a different approach focused on displacing the sodium ions. Applying gypsum, which is calcium sulfate, is highly effective because the calcium component replaces the sodium attached to the soil particles. Once displaced, the sodium can then be leached deeper into the soil profile and away from the grass roots through repeated, deep watering. An application rate of 20 to 40 pounds of gypsum per 100 square feet is recommended for salt-damaged areas.
Repairing Dead Patches
After the chemical threat has been neutralized and the soil has been flushed, repair any resulting dead patches. Remove the dead grass and prepare the soil for new growth by lightly amending it with fresh topsoil or compost. Reseeding or sodding with a turf variety that has a higher tolerance for salt, such as Bermuda grasses or Zoysia, can help the lawn better withstand future accidental exposure.