Lime is one of the most over-applied lawn products. It fixes one thing, acidic soil, and does nothing for a lawn that is already at the right pH. Before you buy a bag, find out what your soil actually is.
What soil pH does grass like?
Most lawn grasses, including Kentucky bluegrass, tall fescue and perennial ryegrass, do best between 6.0 and 7.0. Fine fescues tolerate more acidic soil. Centipede grass is the odd one out: it prefers acidic soil, so do not lime it without a test.
Below about 6.0, nutrients like phosphorus become harder for roots to use, and grass thins. Above about 7.5, iron becomes harder to take up, and lawns can yellow even when fed.
Where are lawn soils acidic, and where are they not?
Soils in the Southeast, the Northeast and the Pacific Northwest are often acidic, because rain leaches calcium out over time. Much of the Midwest and the West sits on limestone or dry, alkaline soils. Chicago-area lawns, for example, are often neutral or slightly alkaline. That is why testing beats advice from a store two states away.
How do you test soil pH?
Take 10 to 15 small cores, 3 to 4 inches deep, from across the lawn, mix them and send a cup of soil to a lab. Your state Cooperative Extension can recommend one. A lab report gives the pH, the lime or sulfur rate per 1,000 sq ft, and nutrient levels. Home kits and probe meters are fine for a rough check but less reliable.
What a Green Lawn charts the readings you log and flags anything outside 6.0 to 7.0:
The card appears once you have logged at least two pH readings in the Log tab. Below 6.0 it suggests garden lime, above 7.0 it suggests sulfur or an acidifying fertilizer.
How much lime per 1,000 sq ft?
It depends on your soil type and how far the pH needs to move. Clay soils need more lime than sandy soils to shift the same amount, so use the rate on your soil test. Many Extension services advise not to spread more than about 50 lbs per 1,000 sq ft at a time; split larger corrections between fall and spring.
The app’s amounts card shows garden lime at a single flat rate for your mapped lawn:
That works out to about 20 lbs per 1,000 sq ft, a single maintenance application rather than a rate scaled to your soil. The line only shows while your soil is acidic or untested: once you log a pH of 6.0 or higher, the card drops it. The Chicago example at pH 7.0 needs no lime at all, and with its readings logged the app shows none.
When is the best time to lime a lawn?
Fall is best. Freeze and thaw cycles over winter work the lime into the soil, and it has months to act before spring growth. Early spring works too. Spreading right after core aeration gets more lime into the root zone. Avoid frozen ground and heavy rain.
What if your soil pH is too high?
Elemental sulfur lowers pH, slowly and only a little at a time. Ammonium sulfate fertilizer helps a little too. On alkaline soils, yellowing grass often responds to iron rather than to a pH fix. See moss in the lawn for how iron products behave, and how to measure your lawn to get the square footage right.
Log each soil test in What a Green Lawn, and the pH card shows whether your lime is actually moving the number.