Soil pH in St. Louis, MO: Lime or Sulfur?

Typical topsoil pH in St. Louis, MO

Typical topsoil in St. Louis, MO is pH 6.09, already right for vegetable garden (6-7). Test before adding anything.

What St. Louis needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, strawberries, roses, pink hydrangeas.
• Just outside, test first: tomatoes (off by 0.1), potatoes (off by 0.1), azaleas and rhododendrons (off by 0.1).
• Sulfur: blueberries 2.5 lb/100 sq ft over 2 applications; blue hydrangeas 1.8 lb/100 sq ft.

What to do next

If your test lands near 6.09, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, potatoes, strawberries, roses, azaleas and rhododendrons, pink hydrangeas.

How mixed the soil is

Of the 238,055 surveyed acres in St. Louis, MO, 43% are moderately acidic (5.5-6.5), 25% are near neutral (6.5-7.3), 21% are strongly acidic (below 5.5), 11% are alkaline (above 7.3). Mapped soils run from pH 4.9 to 8, a spread of 3.1 units across 266 soil components. No single class covers 60% of the county, so two gardens a few miles apart here can need opposite treatments. Test your own bed.

Clay, organic matter and rates

Topsoil here averages 20.7% clay and 2.24% organic matter, which this site treats as loam. Moving it one pH unit takes about 7 lb of lime or 2.3 lb of sulfur per 100 sq ft. 5% of mapped components carry free carbonate (lime already in the ground).

St. Louis against the rest of Missouri

pH 6.09 is right at the Missouri median of 6.13. 53 of 114 Missouri counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Scott (6.03), Franklin (6.05), Osage (6.06), Cole (6.08), Randolph (6.1), Jasper (6.12), Henry (6.13), Callaway (6.14).

The range in Missouri runs from Carter at 5.08 to Knox at 6.71; St. Louis sits 62% of the way up.