How much lime does my lawn need?
It depends on two things: how far the pH has to rise, and how hard the soil resists — its buffering capacity, which tracks clay and organic matter. A sandy soil moves a full pH unit on 25 lb of lime per 1,000 sq ft; a clay soil needs 75. That's why a pH number alone only gets you an estimate, and why a soil test reports a second number, buffer pH, that measures the resistance directly and turns into a lime recommendation in pounds. When you have that, use it. When you don't, this is the rule of thumb every extension office prints.
A loam lawn at pH 5.8 with a 6.5 target: 0.7 × 50 = 35 lb per 1,000 sq ft, or 175 lb on 5,000 sq ft — 5 forty-pound bags. At pH 5.0 the same lawn wants 75 lb per 1,000, which is two applications six months apart, not one.
Lime rates by soil pH and texture
| Current pH | Sandy | Loam | Clay |
|---|---|---|---|
| 5.0 | 37.5 lb | 75 lb (2 apps) | 112.5 lb (3 apps) |
| 5.5 | 25 lb | 50 lb | 75 lb (2 apps) |
| 6.0 | 12.5 lb | 25 lb | 37.5 lb |
| 6.2 | 7.5 lb | 15 lb | 22.5 lb |
Pounds of 100%-CCE limestone per 1,000 sq ft to reach pH 6.5. Split anything over 50 lb into applications six months apart. Rules of thumb from Clemson HGIC and Penn State; the soil test's buffer pH replaces them.
What pH should a lawn be?
Most turf is happiest between 6.0 and 7.0, where nitrogen, phosphorus and potassium are all available; the calculator targets 6.5 for cool-season grasses and 6.3 for warm-season, which tolerate slightly more acid (centipede actually prefers 5.5 and is one of the few lawns you can hurt by liming). Below about 5.5, fertilizer stops working properly — the nitrogen you paid for stays locked up — which is the real reason to lime: not because the grass "likes" lime, but because everything else you do works better at the right pH.
The folk belief is that moss means acid soil and lime kills moss. Moss means shade, compaction and wet soil; it grows at any pH. Liming a lawn that doesn't need it wastes money and can push pH past 7, where iron and manganese lock up and the grass yellows. The same goes for the "sweeten the soil every spring" habit — lime is a correction, not a fertilizer. Test, then lime if the test says so, then retest in a year.
Which lime: pelletized, pulverized, calcitic, dolomitic
- Pelletized — pulverized lime bound into prills so it spreads from a broadcast spreader without dust. Costs more per pound; same chemistry. What most homeowners should buy.
- Pulverized / ag lime — the cheap bulk powder; works faster per pound because it's finer, but it's miserable to spread by hand and blows away.
- Calcitic vs dolomitic — both raise pH; dolomitic also adds magnesium. Use dolomitic only if the soil test shows low magnesium; otherwise calcitic.
- Hydrated (slaked) lime — fast, caustic, easy to overdo. Not for lawns.
- CCE matters. Rates assume 100% calcium carbonate equivalent; a 90% CCE bag needs 55.6 lb to do the work of 50. It's on the label — the calculator takes it.
How much lime for my lawn size?
| Lawn | Lime (loam, pH 5.8 → 6.5) | 40 lb bags | Applications |
|---|---|---|---|
| 2,500 sq ft | 88 lb | 3 | 1 |
| 5,000 sq ft | 175 lb | 5 | 1 |
| 7,500 sq ft | 263 lb | 7 | 1 |
| 10,000 sq ft | 350 lb | 9 | 1 |
Engine figures for one common case; the calculator does yours. 100% CCE; adjust up for the bag's actual CCE.
When and how to apply lime
Fall is best — freeze-thaw cycles work it into the soil over winter and it's ready by spring — but lime can go down any time the ground isn't frozen. Spread it with a broadcast spreader (pelletized) in two crosswise passes, and never more than 50 lb per 1,000 sq ft at once: more sits on the surface, and the top inch of soil jumps past 7 while the root zone hasn't moved. Core aeration first helps. Don't apply lime and fertilizer the same day (ammonium nitrogen reacts with fresh lime and gasses off); give it a couple of weeks. Then wait — lime takes six to twelve months to finish working. Retest before adding more.
Lowering pH: sulfur
The reverse problem — alkaline soil, pH 7.5 and up, common in the arid West and wherever there's limestone — is fixed with elemental sulfur, which soil bacteria slowly turn into sulfuric acid. It's slower than lime (months to a year), and it burns if you overdo it, so the cap is 10 lb per 1,000 sq ft per application. Rates to drop to 6.5:
| Current pH | Sandy | Loam |
|---|---|---|
| 7.0 | 6 lb (1 apps) | 9 lb (1 apps) |
| 7.5 | 12 lb (2 apps) | 18 lb (2 apps) |
| 8.0 | 18 lb (2 apps) | 27 lb (3 apps) |
Elemental sulfur per 1,000 sq ft (12 / 18 / 25 lb per pH unit for sand / loam / clay). Soils over limestone may not move at all — the carbonate buffers it — and you live with 7.5 and choose tolerant grass.
Sources: Clemson HGIC 1650, Changing the pH of Your Soil; Penn State Extension, Liming Turfgrass Areas; UMass Extension, Soil pH and Liming; Virginia Cooperative Extension, Sources of Lime for Acid Soils (CCE).