How to Test Soil pH for Your Lawn: Sampling, Results and Lime Rates

The pH scale is logarithmic, so soil at pH 5.0 is ten times more acidic than soil at pH 6.0 and a hundred times more acidic than soil at 7.0. Small numbers represent big chemical differences. Most lawn grasses grow best between pH 6.0 and 7.0, where the widest range of nutrients is available and soil microbes that break down thatch and release nitrogen are most active.

• Below about 5.5: phosphorus, calcium and magnesium availability drops, aluminum and manganese can reach levels that injure roots, and fertilizer response is poor. Thin turf and moss often move in.
• 6.0 to 7.0: the target for most lawns.
• Above about 7.5: iron and manganese become less available, causing yellowing between leaf veins, and phosphorus can tie up again.

Some grasses prefer the edges of that range, which is covered in the grass table below.

Use a lab test when you plan to lime, fertilize a problem lawn or start a new one. Your state's land-grant university extension service runs or recommends a soil testing lab, with fees that are usually modest; check your state extension website for mailers and instructions. Home kits are fine for quick checks between lab tests, but most do not measure buffer pH, which is what a lime rate depends on.

You can sample any time the ground is not frozen or saturated, but late summer to fall is the most useful time for lawns. Results come back in time for fall liming, and lime then has winter freeze-thaw cycles and months of rain to start working before spring growth. Sample at about the same time of year each time you test so results are comparable, since pH drifts a little with season and moisture.

Wait several weeks after fertilizing and a few months after liming before sampling, so fresh granules do not skew the reading. Test a new lawn area before seeding or sodding, when you can still mix lime into the soil.

A lab report typically lists several numbers. Here is what the ones that matter for lime and fertilizer mean:

• Soil pH (water pH): the current acidity. This tells you whether you need lime (below about 6.0 for most grasses), sulfur (well above 7.0 for most grasses) or nothing.
• Buffer pH (lime requirement index): measures the soil's reserve acidity. It tells the lab how much lime it takes to move the pH. It appears only when lime may be needed.
• CEC (cation exchange capacity): how much the soil holds onto nutrients. Low CEC usually means sandy soil that changes pH easily; high CEC means clay or organic soil that resists change.
• Phosphorus and potassium: usually reported as low, medium, optimum or high, with a fertilizer recommendation. If both are optimum, a zero-phosphorus maintenance fertilizer is the right buy; see how to read a fertilizer label.
• Calcium and magnesium: these help choose between dolomitic lime (adds magnesium) and calcitic lime (mostly calcium).
• Lime recommendation: most labs convert everything into pounds of ground limestone per 1,000 sq ft for lawns. Use that number over any general table.

Two lawns can both test at pH 5.5 and need very different amounts of lime. Soil pH measures only the acidity in the soil water. Clay and organic matter hold a large reserve of acidity on their particle surfaces that releases as you neutralize the water, so they need much more lime to move one unit. Sandy soils hold little reserve and change quickly. Buffer pH captures that reserve. The lower the buffer pH, the more lime the soil needs.

This is why home kits that report only pH cannot tell you how much lime to apply, and why guessing often leads to either no visible change or overshooting. Without a lab buffer test, the conservative approach is to use the texture-based estimates below, apply no more than 50 lb per 1,000 sq ft at a time on established turf and retest before adding more.

These are general planning estimates for ground or pelletized agricultural limestone to raise the pH of the top few inches of lawn soil by one unit. Use your soil test's lime recommendation when you have one. On established turf, apply no more than about 50 lb per 1,000 sq ft per application and split larger amounts across seasons, commonly fall and spring. The lime rate chart covers more starting points.

Pelletized limestone is ground limestone pressed into pellets with a binder, so it spreads cleanly through a lawn spreader without dust and dissolves into powder after rain or watering. The chemistry and rate by weight are essentially the same as powdered agricultural lime. Choose by your soil test's magnesium result:

• Dolomitic lime supplies calcium and magnesium. Use it when magnesium is low or medium. The Old Castle Pro Pelleted Dolomitic Limestone is a plain 50 lb bag meant for a standard spreader.
• Calcitic lime supplies mostly calcium. Use it when magnesium is already high.
• Soluble calcium products such as Jonathan Green Mag-I-Cal for acidic soil are applied at much lower rates; Jonathan Green says one bag has the pH-raising power of up to 15 bags of limestone. Follow the product label, not the limestone table.
• Gypsum does not raise pH. The Andersons NutraSoft pelletized gypsum is pH-neutral and is used for clay structure and salt damage instead.

Check your spreader: Chapin notes its 8401C push spreader is not recommended for pelletized lime. A tow-behind like the Brinly 40 in. combo aerator spreader can drop lime while it perforates the soil. More options are in best lawn spreaders.

Lowering pH is slower and harder than raising it. The usual tool is elemental sulfur, which soil bacteria convert to acid over weeks to months, fastest in warm, moist soil. Many extension services advise applying no more than about 5 lb of elemental sulfur per 1,000 sq ft at a time to established turf, in cool weather and watered in, because higher rates burn grass. Use an elemental sulfur product at its label rate, and retest before repeating.

• Fertilizers containing ammonium sulfate acidify soil gradually and can help hold pH down over years.
• Aluminum sulfate is not a good lawn choice; heavy use can build aluminum to levels that injure roots.
• Soils in arid regions that contain free calcium carbonate (they fizz when a drop of vinegar hits them) are impractical to acidify. Choose grasses adapted to alkaline soil and use iron products for color.

These are approximate preferred ranges drawn from common university extension guidance. Grasses survive outside them, but color, density and fertilizer response suffer. Centipedegrass is the notable exception to liming toward 7.0; see the centipedegrass page. Cool-season details are on the Kentucky bluegrass and tall fescue pages.

Lime works slowly because it has to dissolve and react with the soil. Pelletized lime breaks down faster than coarse lime, but noticeable pH change in the top few inches of an established lawn commonly takes several months, and full effect can take a year or more. Surface-applied lime moves down slowly, which is why liming after core aeration helps. Soluble calcium products act faster, as their makers note, but still need time.

• While correcting pH: retest about a year after the first application, before applying more.
• Once pH is in range: retest every two to three years. Rain, irrigation and nitrogen fertilizer slowly acidify most lawn soils again.
• Anytime a problem appears: retest if the lawn yellows, thins or stops responding to fertilizer.