Soil pH in Polk, MO: Lime or Sulfur?

Typical topsoil pH in Polk, MO

Typical topsoil in Polk, MO is pH 6.02, already right for vegetable garden (6-7). Test before adding anything.

What Polk needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, strawberries, roses, pink hydrangeas.
• Just outside, test first: tomatoes (off by 0.2), potatoes (off by 0), azaleas and rhododendrons (off by 0).
• Sulfur: blueberries 2.3 lb/100 sq ft over 2 applications; blue hydrangeas 1.8 lb/100 sq ft.

What to do next

If your test lands near 6.02, 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 403,294 surveyed acres in Polk, MO, 49% are moderately acidic (5.5-6.5), 31% are near neutral (6.5-7.3), 20% are strongly acidic (below 5.5). Mapped soils run from pH 4.2 to 7.3, a spread of 3.1 units across 201 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 16.3% clay and 2.95% 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. None of the mapped components carry free carbonate.

Polk against the rest of Missouri

pH 6.02 is 0.11 below the Missouri median of 6.13. 47 of 114 Missouri counties have more acidic topsoil. Nationally it is more acidic than the US county median of 6.05.

Closest in pH within the state: Lawrence (5.93), Cape Girardeau (5.97), Morgan (5.99), Greene (6), Dunklin (6.03), Scott (6.03), Franklin (6.05), Osage (6.06).

The range in Missouri runs from Carter at 5.08 to Knox at 6.71; Polk sits 58% of the way up.