Soil pH in Dallas, IA: Lime or Sulfur?

Typical topsoil pH in Dallas, IA

Typical topsoil in Dallas, IA is pH 6.57, already right for vegetable garden (6-7). Test before adding anything.

What Dallas needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, roses.
• Just outside, test first: strawberries (off by 0.1), pink hydrangeas (off by 0.1).
• Sulfur: potatoes 2.5 lb/100 sq ft over 2 applications; blueberries 3.7 lb/100 sq ft over 2 applications; azaleas and rhododendrons 3 lb/100 sq ft over 2 applications; blue hydrangeas 3 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.57, 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 371,767 surveyed acres in Dallas, IA, 49% are moderately acidic (5.5-6.5), 32% are near neutral (6.5-7.3), 19% are alkaline (above 7.3). Mapped soils run from pH 5.7 to 8.2, a spread of 2.5 units across 214 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 25% clay and 4.52% 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. 19% of mapped components carry free carbonate (lime already in the ground).

Dallas against the rest of Iowa

pH 6.57 is 0.21 above the Iowa median of 6.36. 76 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: Polk (6.53), Mills (6.54), Hardin (6.56), Osceola (6.56), Franklin (6.57), Cerro Gordo (6.59), Story (6.59), Worth (6.6).

The range in Iowa runs from Van Buren at 6.02 to Monona at 7.11; Dallas sits 50% of the way up.