Pool water can significantly damage or kill grass, depending on the volume spilled and the type of sanitizing chemical used. While a few splashes are generally harmless, a substantial spill or improper draining can result in brown, dead patches on a lawn. The chemical agents, specifically chlorine and salt, interfere with the grass’s biological processes through distinct mechanisms. Understanding these effects is the first step in protecting a landscape from unintended damage.
How Chlorine Affects Grass and Soil
Standard swimming pool water contains chlorine, typically maintained at 2 to 4 parts per million (ppm). This disinfectant can directly cause chemical burn when concentrated water contacts the grass blades. The resulting damage manifests quickly as yellowing or browning because the chemical bleaches the chlorophyll necessary for photosynthesis.
A large volume of chlorinated water soaking into the soil also causes chemical changes that affect root health. High chlorine concentrations can temporarily disrupt the soil’s microbial balance, which is responsible for cycling nutrients. Pool chemicals can also alter the soil’s pH balance, making it difficult for grass roots to absorb essential nutrients. This chemical stress hinders the grass’s ability to grow and recover.
The Unique Problem of Saltwater Pools
Saltwater pools use a chlorine generator to convert salt (sodium chloride) into chlorine, but they maintain a high salinity level that poses a long-term threat to grass. The primary damage mechanism is osmotic stress, often referred to as “salt burn.” When saline pool water enters the soil, the salt concentration outside the grass roots becomes higher than the moisture inside the plant cells.
This imbalance causes water to be drawn out of the grass roots and leaves, dehydrating the plant even when the soil appears moist. The grass blades may turn a darker green or blue-green color before wilting and turning brown. Over time, chronic salt buildup can damage the soil structure by causing clay particles to clump together, leading to compaction. This compaction reduces aeration and hinders the soil’s ability to drain water, making it harder for the grass to absorb moisture and nutrients.
Immediate Steps for Lawn Recovery
If a pool water spill has occurred, the most immediate action is to dilute and flush the affected area with fresh water. Using a garden hose, deeply soak the spill zone to wash the chemicals—whether chlorine or salt—out of the grass’s root zone. This leaching process must be thorough and may require multiple applications over several hours or days to effectively lower the concentration of harmful substances.
For saltwater spills specifically, rinsing the grass blades with fresh water is important because salt, unlike chlorine, does not dissipate into the air. Once the area is flushed, gently rake the damaged grass to lift flattened blades and improve airflow. If the grass does not recover after a week or two, aeration and reseeding the dead patches may be necessary to restore the lawn.
Safe Pool Draining Practices
Preventing damage during intentional pool draining requires reducing the chemical strength of the water before release. Stop adding chlorine or other chemicals several days before draining to allow them to naturally dissipate. Exposing the water to sunlight for at least a few days helps break down residual chlorine, ideally reducing it to near zero or below 0.1 ppm.
The pool water’s pH should also be checked and adjusted to a neutral range (typically between 7.0 and 7.8) to prevent soil pH imbalance. When draining, direct the hose to different, less-sensitive areas of the yard and move it frequently to prevent waterlogging or chemical buildup. Draining the pool slowly over several days, rather than all at once, allows the soil to absorb the water gradually and minimizes the risk of overwhelming the grass.