How to Soil Test Your St. Augustine Lawn (Start Here)

Why test first

Every fertilizer, iron, and lime decision is a guess without a soil test. Many Gulf Coast lawns already have plenty of phosphorus but run short on other nutrients, or have a high pH that locks up iron and turns grass yellow. A test tells you which of those is true for your yard. A few dollars spent on a test often saves you from buying the wrong bag of fertilizer all season.

It's also the best way to troubleshoot a lawn that won't respond: grass that stays pale after feeding, thin areas that never fill in, or yellowing that looks like iron deficiency.

What a soil test tells you

• pH: how acidic or alkaline the soil is. It controls which nutrients the grass can actually absorb.
• Major nutrients: phosphorus and potassium levels, the second and third numbers on a fertilizer bag.
• Other nutrients: depending on the test, things like calcium, magnesium, sulfur, iron, and zinc.
• Recommendations: most tests suggest what to apply and how much, based on your grass type.

Nitrogen is the exception. It moves through soil quickly, so most home tests don't give a reliable reading for it. Plan on following a nitrogen schedule like the Turf Method calendar regardless.

Which test to use

See our picks on the Gear page, and the university lab on the Tools page. The MySoil kit is the easiest way to start.

How to take a good sample

1. Pick the area. Sample the front and back lawns separately if they're treated differently, look different, or one is shadier. Skip beds, bare dirt, and spots where fertilizer recently spilled.
2. Gather tools. A clean trowel or soil probe and a clean plastic bucket. I pull cores with a stainless soil probe. Every core comes out the same depth. Avoid galvanized or rusty metal buckets, which can throw off the results.
3. Take 15 to 20 small samples scattered across the area in a zig-zag. Each should be a thin slice or core about 3 inches deep, the root zone of a lawn.
4. Remove the grass and thatch from the top of each sample. You want soil, not plant material.
5. Mix everything well in the bucket and break up clumps.
6. Fill the sample bag or box with about a pint (roughly 2 cups) of the mixed soil. Let very wet soil air-dry on paper first; don't dry it in an oven.
7. Label it and list your grass as St. Augustine so the recommendations fit your lawn.

When to test

Late winter is ideal: you'll have results back before the spring feeding. Avoid sampling for a couple of months after fertilizing or liming, which can skew the numbers. After your first test, retesting every year or two is plenty, or anytime the lawn isn't responding the way it should.

What to do with the results

• Phosphorus already high? Choose a fertilizer with a low or zero middle number.
• Potassium low? Lean on a potassium-forward fall fertilizer.
• pH high (alkaline)? Expect iron issues. Plan on liquid iron in the growing season and slowly lowering pH with compost and sphagnum peat moss. See iron for St. Augustine.
• pH low (acidic)? Less common here. Follow the report's lime recommendation.

Not sure how to read your report? Email it to hello@turfmethod.com.