Does Salt Kill Weeds and Grass? The Dose and Soil Math

The tablespoons are our conversions, not kitchen experiments. We turned the kg per hectare in published trials into grams and spoons at USDA’s 18 g per tablespoon, then ran the same grams through USDA Agriculture Handbook 60, the soil salinity manual. Result: 1 tablespoon per sq ft mixed through 6 inches of loam adds about 3.6 dS/m, just under the 4 dS/m line that defines a saline soil. Enter your own dose in the calculator below.

How much salt kills which weed

The range runs about 46 to 1 from a young annual grass to a deep perennial, which is why “salt works” and “salt did nothing” are both reported. Rates are as published; the spoon and soil columns are our arithmetic (download the data).

Published rate	Grams per sq ft	Table salt equivalent	ECe added, top 6 in of loam (dS/m)	What happened	Source
488 kg/ha, repeated, fine salt	4.5	1/4 tbsp per pass	0.9	Sourgrass: 92 and 96% control at 6 weeks, 2007 and 2008	Brosnan 2009
488 kg/ha, 3 weekly passes	4.5	1/4 tbsp per pass	0.9	Goosegrass: under the 70% bar, slightly over 50% at 8 weeks, and injury faded by 6 weeks	Brosnan 2009; co-author note
488 kg/ha, common bermudagrass	4.5	1/4 tbsp	0.9	The lawn grass itself: over 20% injury	McCullough 2011
976 kg/ha, one pass	9.1	1/2 tbsp	1.8	Smooth crabgrass at the tillering stage: 90 to 100% control, 7 to 28 days. Seashore paspalum injury 0 to 6%; bermudagrass over 20%	McCullough 2011
1,464 kg/ha, one pass, fine salt	13.6	3/4 tbsp	2.7	Sourgrass: 84% one year, 23% the next	Brosnan 2009
1,952 kg/ha, one pass	18.1	1 tbsp	3.6	Rate required for excellent control of younger, multileaf crabgrass	McCullough 2011
8 tons per acre	167	9 tbsp	33	Stopped sprouts from green stumps; killed poison ivy and shrubs (Rudolfs 1921)	Harper 1940
1/2 to 2 lb per sq ft	227 to 907	13 to 50 tbsp	Over 45	The usual rate for eradicating vegetation, as of 1940	Harper 1940
20 tons per acre	417	23 tbsp (1.4 cups)	Over 50	Needed for bindweed at Hays, Kansas; 1918 plots grew nothing but Russian thistle for 10 years	Harper 1940
About 1 lb per plant	454 per plant	1.6 cups per plant	Not applicable	Spurge nettle: 2 of 28 marked plants reappeared by October 1940	Harper 1940

The trials explain the split. Dry salt on leaves burns tissue, so small grasses die at spoon doses, and WSU Extension warns that weeds and grasses with good root systems recover from contact burn. Killing the roots is a different job: Harper describes salting enough to reach perennial roots 4 feet down, and photographs a spurge nettle root 72 inches long. If your weed is dandelion, we found no published salt rate at all: it sits somewhere on this ladder and we could not find anyone who has measured where. Our common lawn weeds guide helps you place yours by type.

Boiling water burns leaves the same way without leaving salt behind, and our review of whether boiling water kills weeds converts hot-water trial doses to ounces per square foot.

What one tablespoon does to the top 6 inches of soil

Salinity is measured as ECe, the electrical conductivity of water pulled from a saturated soil paste. Handbook 60 (p. 1) calls soil saline at 4 dS/m (its mmhos/cm) and sets the sodium line at an exchangeable sodium percentage (ESP) of 15. Its conversion, 640 mg of salt per liter per dS/m (p. 16), turns grams into ECe. Here is 18 g worked through three soils.

Step, for 1 tablespoon (18 g) per sq ft	Sandy	Loam	Clayey	Input
Soil in 1 sq ft, 6 in deep (kg)	21.2	18.4	17.0	0.5 cu ft at an assumed 1.5, 1.3 and 1.2 g per cm³
Water at saturation (liters)	6.8	7.8	10.1	Average saturation percentage 31.8, 42.5, 59.5 (Handbook 60, Table 1)
Salt in that water (mg per liter)	2,665	2,301	1,781	18,000 mg divided by liters
ECe added, mixed through 6 in (dS/m)	4.2	3.6	2.8	Divide by 640
ECe added if it stays in the top 2 in (dS/m)	12.5	10.8	8.3	One third of the soil, so 3 times the strength
Chloride (mg per kg of soil)	514	593	643	NaCl is 60.66% chloride by weight
Starting SAR	29	25	19	Assumes 5 meq per liter of calcium plus magnesium, before exchange
ESP added, at most (points)	29	11	6	308 meq of sodium, all held by the soil; assumed exchange capacity 5, 15 and 30 meq per 100 g

Three readings matter. Plant roots see more than the ECe figure, because the soil solution at the wet end of the field range is about twice the paste concentration (Handbook 60, p. 8). A loose tablespoon that rain carries only 2 inches down reaches about 11 dS/m in loam, close to the 12 dS/m where FAO puts tall fescue and perennial ryegrass at half yield. And on sand the sodium math can cross ESP 15 at about 1/2 tablespoon, though sand also drains salt fastest.

1. 1/4 tbsp (4.5 g)0.90
2. 1/2 tbsp (9 g)1.80
3. 1 tbsp (18 g)3.60
4. 2 tbsp (36 g)7.20
5. 4 tbsp (72 g)14.40

Source: Green Industry Report arithmetic from USDA Handbook 60 inputs Saline soil line is 4 dS/m. Values match the worked table; 43 dS/m is close to the limit of the 640 conversion.

Show the numbers

	Mixed through top 6 in	Held in top 2 in
1/4 tbsp (4.5 g)	0.90	2.70
1/2 tbsp (9 g)	1.80	5.40
1 tbsp (18 g)	3.60	10.80
2 tbsp (36 g)	7.20	21.60
4 tbsp (72 g)	14.40	43.10

Salt per sq ft, in grams (1 tablespoon = 18 g, 1 cup = 292 g) (g per sq ft)Salt type (Nov. 2026 listings)Rock salt, 50 lb ($10.67 to $13.06)Pool salt, 40 lb ($9.78 to $10.99)Softener crystals, 50 lb ($7.49, one co-op)Table salt, 26 oz boxes ($11.04 for 12)

ECe added, sandy soil, top 6 in (dS/m)

4.2

ECe added, loam, top 6 in (dS/m)

3.6

ECe added, clayey soil, top 6 in (dS/m)

2.8

ECe added, loam, if held in top 2 in (dS/m)

10.8

ESP points added, loam, at most

11.2

Water to dilute its chloride to 250 mg per liter (gallons per sq ft)

11.5

Salt cost to treat 1,000 sq ft at this dose$10 to $10

Compare with the 4 dS/m saline line and the grass table on this page. Arithmetic with stated assumptions, not a soil test; values above about 50 dS/m are rough.

Worked example at the default: 18 g per sq ft gives 4.2, 3.6 and 2.8 dS/m in sandy, loam and clayey soil. A 50 lb bag at that dose covers about 1,260 sq ft. Results above about 50 dS/m are rough, since the 640 factor was not built for near-brine soil water.

Does salt kill grass?

Yes, and leaf burn can come before soil salinity matters. McCullough and Raymer measured over 20 percent injury on common bermudagrass at 4.5 g per sq ft, about 1/4 tablespoon, even though bermudagrass ranks among the most salt-tolerant lawn grasses. Of the two turf grasses in that trial, only seashore paspalum took a weed-killing dose with little damage. UF/IFAS LH005 rates it excellent for salt and bahiagrass very poor, the last of seven Florida lawn grasses.

Grass	CSU: growth problems start (dS/m)	FAO: ECe at 100% / 50% / 0% yield	Tablespoons per sq ft to reach CSU low end, 6 in of loam	Same, top 2 in only
Kentucky bluegrass	3 to 6	Not listed	0.8	0.3
Buffalograss	3 to 6	Not listed	0.8	0.3
Blue grama	5 to 6	Not listed	1.4	0.5
Perennial ryegrass	8 to 10	5.6 / 12 / 19	2.2	0.7
Turf-type tall fescue	8 to 10	3.9 / 12 / 20	2.2	0.7
Fine fescue	8 to 12	Not listed	2.2	0.7
Bermudagrass	16 to 18	6.9 / 15 / 23	4.5	1.5
Alkaligrass (Fults, Seasalt)	20 to 30	Not listed	5.6	1.9

The two tables disagree: CSU puts bermudagrass at 16 to 18 dS/m, while FAO starts its yield loss at 6.9 and notes common types run about 20 percent less tolerant. CSU is rating lawn use and FAO forage yield, so plan on the lower number if the grass is staying.

How long does salt stay in soil?

Until water carries it out, since salt does not break down. CSU Extension’s table gives the rule: 6 inches of clean water removes 50 percent of soluble salts, 1 foot removes 80 percent and 2 feet removes 90 percent, in soil that drains. One foot over 1 sq ft is 7.5 gallons. So “permanent” is wrong, and so is “a few rains.”

Source: CSU Extension, Growing Turfgrass on Salt-Affected Sites, Table 2 Remaining percent is 100 minus CSU's stated reduction; 0 inches is the starting point. Applies only to soil with good internal drainage.

Show the numbers

	Salt remaining, percent
0 in	100
6 in	50
12 in	20
24 in	10

City	Normal rain, inches per year	Months for 6 in to fall	Months for 1 ft to fall
Miami	67.41	1.1	2.1
Atlanta	50.43	1.4	2.9
Boston	43.59	1.7	3.3
Seattle	39.34	1.8	3.7
Dallas-Fort Worth	37.01	1.9	3.9
Minneapolis	31.62	2.3	4.6
Denver	14.48	5.0	9.9
Los Angeles	14.25	5.1	10.1
Phoenix	7.22	10.0	19.9

Published cases bracket the range. On deep Oklahoma sand, Harper found only 1 of 6 spots still held an appreciable salt concentration 16 or 28 months after a 10 to 40 ton per acre dose. On the Kansas plots, a 20 ton per acre dose kept out everything but Russian thistle for 10 years. Virginia Tech says significant buildup is uncommon where rain tops 20 inches a year; CSU Pueblo says a pinch leaves soil uninhabitable for several months.

Clay holds a second problem after the salt is gone. Sodium replaces calcium on clay particles, and Harper notes sodium clay absorbs rain more slowly, which slows its own removal. In sodic soil, ESP 15 or more by Handbook 60, CSU warns that leaching can worsen drainage, so test before flushing. Our guide to improving clay soil covers that soil type.

The salt, vinegar and dish soap recipe, traced to evidence

The common mix is 1 gallon of vinegar, 1 cup of salt and a squirt of soap. That is 77 g of salt per liter, about 2.2 times ocean water’s 35,000 ppm. It sounds strong, yet the dose depends on how much reaches the ground.

How the salt goes down	Salt delivered (g per sq ft)	Table salt equivalent	Compared with the 4.5 g trial rate
Recipe sprayed at a vinegar label volume, 44 to 88 fl oz per 1,000 sq ft	0.10 to 0.20	About 1/30 tsp at the high end	20 to 45 times lower
Recipe soaked on, 1 gallon per 100 sq ft	2.9	1/2 tsp	About 1/2 as much
A pinch (0.4 g) on a 3-inch circle	8.2 on that circle	1/2 tbsp rate, tiny area	About 2 times higher
1 cup dry over 10 sq ft	29	1.6 tbsp	About 6 times higher
Recipe poured, 1 quart per sq ft	73	4 tbsp	About 16 times higher

So a mist adds little salt per pass, and the buildup UConn Extension warns about comes from repeating it or from soaking. We found no trial of the three-part kitchen mix. Evidence for each part runs elsewhere: our vinegar weed killer page covers acid strength, Ask Extension says dish soap works but is not the best surfactant, and UF/IFAS EP580 says most of these mixes have not been tested. Bleach has its own page.

Rock salt, table salt, pool salt or Epsom salt?

Salt	What it is	Evidence on weeds	Dated price (Nov. 5, 2026)
Table salt	99% NaCl plus anticaking agent in the trial product; 83% of grains 0.25 to 0.5 mm in that product	Fine grains beat coarse in the 2008 sourgrass ratings	$11.04 for 12 boxes of 26 oz, about $0.57 per lb
Rock salt	Coarse crystals, like loose gravel; road grades run about 98.5% NaCl (Purdue ID-412)	Closest to the trial’s coarse salt, 75% of grains 1 to 2 mm: lower control on 3 of 4 rating dates	$10.67 to $13.06 for 50 lb, about $0.21 to $0.26 per lb
Pool salt	Sold as sodium chloride, same chemistry	No separate trial found	$9.78 to $10.99 for 40 lb, about $0.24 to $0.27 per lb
Softener crystals	Sold as sodium chloride, same chemistry	No separate trial found	$7.49 for 50 lb, about $0.15 per lb, one co-op
Epsom salt	Magnesium sulfate, no sodium; about half the dissolved charge per gram (8.1 vs. 17.1 meq per g)	UGA Extension agent: does not do anything to kill weeds. UConn: excess magnesium interferes with phosphorus uptake	Not priced

Weight is what counts, and sodium chloride is sodium chloride. “Best rock salt for killing weeds” has no answer in the trials beyond grain size: if you use it at all, fine grains give more contact per gram.

Concrete, trees and wells

Concrete and pavers. Chloride migrates through concrete and can start corrosion once it reaches a critical level at the steel, and salt crystals growing in pores can cause damage without any cold weather, says the CP Road MAP Brief, August 2014. In freezing climates dilute brine is the worst case: the standard scaling test uses a 4 percent calcium chloride solution because damage accelerates at about that strength. The 1 cup per gallon recipe is 7.2 percent by weight and gets more dilute as it soaks in. Epsom salt is no clean swap, since magnesium ions can react with cement paste too. Our pavers vs. concrete comparison covers the de-icer ratings.

Trees and shrubs. Purdue ID-412 cites soil under 30 feet from a highway at 890 ppm chloride, ten times the level that inhibits germination and root growth in grasses and wildflowers. One tablespoon per sq ft in 6 inches of loam works out to 593 mg per kg, the same order. Virginia Tech finds road salt builds up within 30 to 50 feet and advises planting sensitive species 50 to 60 feet from salted paving. Injury shows as brown leaf edges and needle tips.

Water. One tablespoon carries 10.9 g of chloride. Leaving in 1 foot of drainage (28 liters), that is about 386 mg per liter, above EPA’s 250 mg per liter secondary drinking water standard and the 230 mg per liter chronic aquatic life criterion. Dose a few weeds and this stays small; salt a whole gravel drive above a shallow well and it does not.

Where salt is acceptable and where it isn’t

Spot	Verdict	The number behind it	Source
Crack or paver joint, nothing wanted within 50 to 60 ft downslope	Acceptable as a spot dose	About 0.4 g per seedling, at most at the trials’ weekly interval	CSU Pueblo; Virginia Tech
Gravel path with bare soil beneath	Only if nothing should grow there	1 cup over 10 sq ft adds about 5.8 dS/m in 6 in of loam	Our arithmetic
Lawn, any common grass	No	Over 20% bermudagrass injury at 4.5 g per sq ft	McCullough 2011
Seashore paspalum turf	Researched, no consumer rate	0 to 6% injury at 9.1 g per sq ft, when timed to tillering crabgrass	McCullough 2011
Garden bed or vegetables	No	Salt is highly mobile and spreads to desired plants	Illinois Extension
Near trees	No	Roadside soil at 890 ppm chloride is ten times the level that inhibits root growth	Purdue ID-412
Above a septic field or shallow well	No	About 386 mg per liter chloride per tablespoon, 1 ft of drainage	Our arithmetic; EPA
Reinforced slab or steel edging	Avoid	Chloride builds to a critical level at the steel	CP Road MAP Brief
Paid landscape job	No	UF/IFAS (Florida): illegal for commercial applicators to apply homemade herbicides; only EPA-registered products	UF/IFAS EP580

1. 1Is anything you want alive within 50 to 60 ft downslope, or a septic field or shallow well nearby?

   YesDo not salt. Pull the weed, or use a registered product and follow its label.

   NoGo to the next question

2. 2Is the weed in a lawn or garden bed?

   YesDo not salt. About 4.5 g per sq ft injured bermudagrass over 20 percent, and salt moves through soil to nearby plants.

   NoGo to the next question

3. 3Is it a deep perennial such as bindweed, thistle or spurge nettle?

   YesSkip salt. Bindweed took about 417 g per sq ft in the Kansas work, and tops regrow from roots below a light dose.

   NoGo to the next question

4. 4Is it a small seedling in a crack or joint, over no reinforcing steel?

   YesA pinch of about 0.4 g at the base is a low-risk try. Wait at least 7 days before repeating, and hand-pull what survives.

   NoHand-pull it, or see our selective herbicide guide for a registered option.

Source: McCullough 2011; Harper 1940; Virginia Tech SPES-342

For lawns, selective herbicides exist because salt cannot tell weed from turf. To clear a whole area for replanting, see how to kill grass before replanting: salt delays the very seed you plan to sow. Other lawn and weed pages are in our Turf and Trees hub.

If you already used too much

1. Sweep up undissolved grains first. Every tablespoon removed is 18 g that never reaches the soil.
2. Flush with clean water: Virginia Tech says 2 inches over 2 to 3 hours, stopping at runoff, and again 2 days later if levels stay high. Two inches is about 1.25 gallons per sq ft.
3. On clay or slow-draining ground, get a lab test before repeated flushing. Ask for ECe and SAR or ESP, the two numbers on this page.
4. Add gypsum only if the test shows sodium. Handbook 60 (p. 49) lists 5.2 tons per acre-foot to replace 3 meq per 100 g. For 1 tablespoon per sq ft in loam that scales to about 30 g of gypsum per sq ft, or 66 lb per 1,000 sq ft, at most. CSU advises against gypsum for ordinary white alkali.
5. Retest before you reseed. Aim below 3 dS/m for Kentucky bluegrass, 8 for tall fescue and 16 for bermudagrass, per CSU’s table, and lower if you can, because germination may be more sensitive.

This page is general information, not legal or pesticide-use advice. Salt carries no herbicide label; any registered product you use instead has one, and the label is the law.