Lime for Northern Lawns: When and How Much

Every fall the garden centers stack bags of lime by the door, and every fall a lot of homeowners buy a few bags because their neighbor does. On the golf course we never put down a pound of lime without a soil test in hand. Lime is a fix for one specific problem: soil that's too acidic. If your soil isn't acidic, lime does nothing for the grass, and in some soils it makes things worse.

What lime actually does

Lime is ground limestone. It raises soil pH, which is a measure of how acidic or alkaline the soil is. Cool-season grasses like Kentucky bluegrass, tall fescue, and perennial ryegrass grow best with a pH of roughly 6.0 to 7.0. Below about 6.0, nutrients like phosphorus get locked up, fertilizer works less well, and moss and some weeds gain ground on the grass.

Lime doesn't feed the grass and it doesn't green it up. It changes the soil chemistry so the fertilizer you already apply can do its job.

Does your lawn need it? Test first

This is the whole game. Soils vary a lot across the northern states:

• Often acidic: much of the Northeast, the Great Lakes snowbelt, the Pacific Northwest, sandy soils, and areas under pine and oak. Lime is common there.
• Often neutral to alkaline: a lot of the Midwest's prairie soils, the Plains, and the mountain West. Many of these lawns already sit at 7.0 or higher and should never be limed.

A soil test from your state's extension lab costs a little and tells you the pH and, just as important, the buffer pH, which is what the lab uses to calculate how much lime it takes to move your soil. Fall is a great time to sample; see fall soil testing and how to read the report.

If the report doesn't recommend lime, don't buy lime.

Calcitic or dolomitic?

• Calcitic lime is mostly calcium carbonate.
• Dolomitic lime also contains magnesium.

Your soil test settles this, too. If magnesium is low, dolomitic makes sense. If magnesium is already high (common in some clay soils), stick with calcitic.

Pelletized or pulverized?

Pulverized lime is a fine powder: cheap, effective, and messy. Pelletized lime is the same powder pressed into pellets that break down with rain and go through a normal lawn spreader without a cloud of dust. For a home lawn, pelletized is worth the extra cost.

How much at once

Your test gives a total amount, usually in pounds per 1,000 square feet. On an established lawn, extension services generally advise putting down no more than about 50 pounds per 1,000 square feet in one application. If the test calls for more, split it: half this fall, half next spring, or spread it over a couple of years. Lime works slowly, mostly in the top inch or two of soil, and large single doses can burn turf or sit on the surface.

Set the spreader by the bag's directions, go over the lawn in two passes at right angles to each other at half the rate, and you'll avoid stripes.

Why fall is the best time

• Rain, snow, and the freeze-thaw cycle work lime down into the soil over the winter.
• The lawn is growing, but not stressed by heat.
• If you core aerate first, some of the lime falls into the holes and gets deeper, faster.

Lime can go down any time the ground isn't frozen, but a fall application is ready to work when the grass wakes up in spring.

What lime won't fix

If your soil pH is already fine, lime won't fix a thin lawn. The usual culprits are shade, compaction, poor drainage, the wrong grass for the spot, or mowing too short. Moss in particular is often blamed on acid soil when the real cause is shade and wet ground; lime alone rarely gets rid of it.

Re-test every few years

Lime lasts, so you don't need it every year. Re-test every two to three years and only lime again when the numbers say so. The most common mistake I see is someone liming the same lawn every fall for a decade until the pH is too high, and then wondering why iron and manganese deficiencies show up as yellow grass.

Pair your lime with the right late-fall fertilizer application and the lawn heads into winter in the best shape it can be.

Related: Moss in the Lawn: What It's Telling You