Soil pH in Sioux, IA: Lime or Sulfur?

Typical topsoil pH in Sioux, IA

Typical topsoil in Sioux, IA is pH 6.2, already right for vegetable garden (6-7). Test before adding anything.

What Sioux needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.
• Just outside, test first: potatoes (off by 0.2), azaleas and rhododendrons (off by 0.2).
• Sulfur: blueberries 4.1 lb/100 sq ft over 3 applications; blue hydrangeas 3.4 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.2, 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 484,509 surveyed acres in Sioux, IA, 62% are moderately acidic (5.5-6.5), 31% are near neutral (6.5-7.3), 7% are alkaline (above 7.3). Mapped soils run from pH 5.7 to 8, a spread of 2.3 units across 198 soil components. 62% of the land falls in one class, so the county figure is a fair first guess for most yards here.

Clay, organic matter and rates

Topsoil here averages 31.1% clay and 4.12% organic matter, which this site treats as clay. Moving it one pH unit takes about 11.5 lb of lime or 3.4 lb of sulfur per 100 sq ft. 6% of mapped components carry free carbonate (lime already in the ground).

Sioux against the rest of Iowa

pH 6.2 is 0.16 below the Iowa median of 6.36. 13 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: Crawford (6.17), Cherokee (6.18), Henry (6.18), Page (6.18), Marion (6.21), Wapello (6.21), Appanoose (6.22), Davis (6.22).

The range in Iowa runs from Van Buren at 6.02 to Monona at 7.11; Sioux sits 17% of the way up.