Soil pH in Pocahontas, IA: Lime or Sulfur?

Typical topsoil pH in Pocahontas, IA

Typical topsoil in Pocahontas, IA is pH 6.73, already right for vegetable garden (6-7). Test before adding anything.

What Pocahontas needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, roses.
• Just outside, test first: strawberries (off by 0.2), pink hydrangeas (off by 0.2).
• Sulfur: potatoes 4.1 lb/100 sq ft over 3 applications; blueberries 5.8 lb/100 sq ft over 3 applications; azaleas and rhododendrons 5.1 lb/100 sq ft over 3 applications; blue hydrangeas 5.1 lb/100 sq ft over 3 applications.

What to do next

If your test lands near 6.73, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.

How mixed the soil is

Of the 367,689 surveyed acres in Pocahontas, IA, 41% are near neutral (6.5-7.3), 33% are moderately acidic (5.5-6.5), 27% are alkaline (above 7.3). Mapped soils run from pH 5.9 to 7.9, a spread of 2 units across 134 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 30.4% clay and 6.36% organic matter, which this site treats as clay. At 6.36% organic matter the soil buffers like a heavier one, which pushes it into the clay bracket. Moving it one pH unit takes about 11.5 lb of lime or 3.4 lb of sulfur per 100 sq ft. 28% of mapped components carry free carbonate (lime already in the ground).

Pocahontas against the rest of Iowa

pH 6.73 is 0.37 above the Iowa median of 6.36. 89 of 99 Iowa counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Palo Alto (6.7), Wright (6.7), Winnebago (6.72), Emmet (6.73), Hamilton (6.74), Boone (6.76), Kossuth (6.78), Humboldt (6.79).

The range in Iowa runs from Van Buren at 6.02 to Monona at 7.11; Pocahontas sits 65% of the way up.