Will Pool Salt Water Kill Grass?

Splash-out and the odd backwash will not kill a lawn. Salt pool water can hurt grass, though, when the same patch takes it over and over, or when a full drain goes onto one spot. The salt does not break down or wash off on its own. It stays in the soil until enough fresh water pushes it below the roots.

The chlorine is the smaller worry. The City of Chandler, Arizona, notes that chlorine in pool water is rapidly inactivated by sunlight. The salt is what lingers. For how the rest of a salt pool works, start at the salt water pools hub.

How salty is pool water, in terms a soil test uses?

Most salt pools run around 3,200 ppm, roughly a tenth of ocean water at about 35,000 ppm. Soil labs and turf guides do not use ppm. They measure electrical conductivity (EC) in dS/m, which is the same number as mmhos/cm.

The University of Georgia’s soil salinity guide gives the conversion: sodium chloride has a TSS of 640 ppm per dS/m. So:

3,200 ppm / 640 = 5.0 dS/m

The factor is not exact, and our sources do not agree on what it applies to. A plant research protocol says the 640 figure is a convention for mixed salts in irrigation water, and puts 10 mM NaCl close to 1 dS/m. 10 mM of salt is 584 ppm. That works out to about 5.5 dS/m for pool water (3,200 / 584 = 5.48). North Dakota State’s extension uses a conversion factor that increases with conductivity for natural water, which would put it at about 4.2 dS/m. Those waters carry a mix of minerals, and pool water is mostly sodium chloride, so we lean on the salt-specific figures. Call it roughly 4 to 5.5 dS/m, and 5 as a working number.

What that means for grass

Colorado State University Extension lists the soil salt level above which noticeable plant growth reduction and management problems normally occur for common turfgrasses:

Utah State’s extension ranks the same grasses in the same order but puts the lines a little lower, placing Kentucky bluegrass in its most sensitive class and tall fescue and perennial ryegrass at 6 to 10. Either way, bluegrass is the one to worry about, and bermudagrass shrugs off far more than a pool can deliver.

One catch. Those numbers are soil EC, measured on a water extract of the soil. They are not the EC of the water you pour on. Rain and deep watering push salt down and out of the root zone. Repeated dumping does the opposite. Chandler warns that watering the same area repeatedly with pool water could build-up an excessive salt level in the soil. A bluegrass lawn that takes every backwash along the same fence line is the classic case.

For scale: the full salt load in a 10,000 gallon pool at 3,200 ppm is about 267 lb (pool salt calculator). A full drain onto one corner puts all of that there.

Sodium is the long-term problem

Salt hurts grass two ways. The University of Georgia says high salt levels hinder water absorption, inducing physiological drought, and that excess salt ions cause their own damage, including leaf tip burning and restricted root growth. Utah State adds that in salty soil turfgrasses extract water less easily, which makes any drought stress worse.

Sodium does extra damage to the soil itself. When sodium builds up, UGA explains, soil particles repel each other instead of clumping, and you get tight, poorly draining ground with a surface crust. Chandler lists what to look for: soil that is dry or dense with a cracked appearance or a grayish-white color, and plants with dead, blotched leaf edges and tips.

Fixing a salty patch

Leach it. Deep watering with fresh water moves salt down. UGA’s rule of thumb: 6 inches of water will remove about half of the salt, 12 inches about 80%, 24 inches about 90%. Colorado State gives the same figures. Apply it slowly so it soaks in rather than running off.

Gypsum only if the soil test says sodium. This is where common advice gets sloppy. Gypsum is calcium sulfate, and it helps when sodium is the problem: Utah State says that where sodium makes up a large share of the salts, additions of gypsum or sulfur may be necessary, so calcium can replace sodium and water can carry it down. For soils that are simply salty, Colorado State says adding gypsum is not recommended. Colorado State also warns that leaching sodic soils that contain high salt levels can make drainage worse. Pool salt is sodium chloride, so a heavily dosed patch could go either way. Get a soil test that reports sodium before buying a bag.

Before you drain: check the rules

Where the water goes is often regulated. Portland, Oregon, prohibits the discharge of heated, chlorinated, or salt-treated waters to storm drains, filter backwash included, and says to use the sanitary sewer or let the water soak into the ground. Chandler bans pipes hard plumbed to discharge off property and prefers discharge kept on your property or sent to the sewer cleanout, with no permit needed for either. Other cities differ. Call your city or county stormwater office before a full drain.

If you do use the yard, Chandler’s advice is simple: drain slowly, and move the discharge hose to different areas of the yard each time. Our guide on how to backwash a salt water pool covers where to point the hose.

Draining because the salt reads high? Test first

Plenty of partial drains start with a high number on the panel. The panel has no salt sensor. It reads how easily current crosses the cell and infers salinity, so a reading can drift while the actual salt stays put. Check with a separate pool salinity tester first. If it really is high, use the tool to lower the salt level in your pool and drain only what you need, which also means less salt on the lawn.

Salt as a herbicide

People use salt as a weed killer on purpose, and it works the same way it hurts your lawn. That is why weed control agencies warn against it. King County’s noxious weed program notes that salt dissolves with water and seeps deeper into the ground, that it can harm surrounding vegetation, and that high concentrations can be toxic to soil organisms. Salt does not stay where you pour it. Treat pool water the same way near beds you care about. For what grows well next to a salt pool, see plants around a saltwater pool. Salty splash also affects hardscape, which is covered in sealing concrete around a salt water pool.

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