Lawn Soil Test Helper

Quick answer: send the sample to the lab your state’s extension service uses. Take 6 to 12 or more small cores from all over the lawn, each 2 to 4 inches deep (the depth your lab asks for), mix them in a clean plastic bucket, and send a cup to a pint. When the report comes back, the lime or sulfur it recommends is a rate per 1,000 square feet: multiply by your lawn’s size and divide by the bag. Then split it. Arkansas and UConn put at most 50 lb of lime per 1,000 sq ft down at one time, Missouri 100, and K-State 5 lb of sulfur.

How to use it

Pick your state first: the lab its extension service sends homeowners to appears under the answer, with its own page for fees, forms and the bag to use. Take the sample the way the guide below the tool says. When the report comes back, choose lime or sulfur, copy the lab’s number and its unit (per 1,000 sq ft, per 100 sq ft, per acre or tons per acre), and type your lawn’s size and the bag you are buying. The answer is the pounds and bags for your whole lawn, then how each source splits it into applications. The link at the bottom keeps all of it, so you can open the same plan in spring.

Why this tool will not guess a lime rate

Most lime calculators take your pH and hand you a number. The labs do not work that way, and for good reason. How much lime it takes to raise the pH by a point depends on the soil’s buffer: a sandy soil moves with a little, a clay soil holds out for a lot. The lab measures that and prints the rate for your soil. For a lawn at pH 5.5 to 5.7, Arkansas’s own table runs from 46 to 115 lb per 1,000 sq ft, depending on how much calcium the soil already holds. A calculator that only knows your pH is guessing inside that range. So this one takes the lab’s number, and without it gives none.

Splitting it: the sources disagree

A lawn can only take so much lime at once, and the sources set the limit in different places:

• Arkansas (Aaron Patton’s Liming Your Lawn): no more than 50 lb per 1,000 sq ft in any one application. Under 50, put it all down in spring or fall. Between 50 and 100, half in spring and half in fall. Over 100, 50 in spring and 50 in fall, then retest before any more.
• UConn: typically 50 lb per 1,000 sq ft at a time, with more in spring and fall or at 30-day intervals.
• Missouri (its own soil lab’s guide): up to 100 lb per 1,000 sq ft at one time, with the rest six months to a year later.

So a report that says 75 lb is one application to Missouri and two to Arkansas and UConn. The tool shows all three for your number. Arkansas also says to water lime in afterwards, so it does not burn the grass. And lime is slow: UConn says it takes 6 to 18 months to move the pH, which is why the retest comes a year later, not a month.

Sulfur is a different job

Lowering the pH is harder than raising it. K-State caps elemental sulfur at 5 lb per 1,000 sq ft per application on an established lawn, in spring or fall, with a retest 6 to 12 months later. It adds that some soils are so well buffered they will not come down at all. Missouri’s lab goes further. On an established lawn, it says, lowering the pH is “usually unrealistic”, because you cannot put enough sulfur down without burning the grass. If your report recommends sulfur, the tool splits it by K-State’s cap and shows Missouri’s warning beside it.

What pH a lawn wants

Here too the published ranges differ. Arkansas puts most lawns at 5.8 to 7.0, centipedegrass at 5.0 to 6.0 and St. Augustinegrass at 6.5 to 7.5. Clemson puts most turfgrasses at 6.0 to 6.5 and centipede at 5.5 to 6.0. K-State says 6.0 to 7.0. Type the pH from your report into the tool and it shows where yours sits against each. That tells you whether the lab’s recommendation makes sense, not how much to use.

How deep to sample — and why it matters

This is the biggest disagreement of all: Clemson says 2 to 4 inches for a lawn, K-State 3, Missouri 3 to 4 (6 for a new lawn), Arkansas about 4, or 4 to 6, and Minnesota’s general guide at least 6. It matters because a lab’s recommendation is calibrated to the depth it expects: lime sits near the surface of an established lawn, so a shallow sample reads it and a deep one dilutes it. Take the depth your lab asks for on its form, skim off the grass and thatch first, and keep the front and back lawns apart if they have been treated differently. Nevada adds one more: do not sample within a month of fertilizing.

Where to send it

Most states have a public lab, usually at the land-grant university and sometimes run by the state department of agriculture (North Carolina’s). Arkansas tests its residents’ soil free, through the county extension office. Kentucky and Ohio take samples through the county office too. In fifteen states the extension service points homeowners to a list of labs rather than one of its own, and the tool links that list. Nebraska’s closed in 2008, and Alaska’s extension says plainly it “does not offer soil testing services”. Rhode Island’s Master Gardeners test pH for free, but that is not a full nutrient test. Whatever lab you use, ask for the lawn or turf recommendation. A lab that sends numbers without one leaves you to guess.

When you have the lab’s nitrogen advice too, the fertilizer rate is the next job. And before you spread anything, get the lawn’s real size from the lawn size calculator, because the bags follow the square feet. If the grass is already struggling, the lawn doctor sorts pH-type yellowing from a dull mower blade, grubs and disease.