Soil pH in Delaware, IA: Lime or Sulfur?

Typical topsoil pH in Delaware, IA

Typical topsoil in Delaware, IA is pH 6.34, already right for vegetable garden (6-7). Test before adding anything.

What Delaware needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.
• Sulfur: potatoes 1.8 lb/100 sq ft; blueberries 3 lb/100 sq ft over 2 applications; azaleas and rhododendrons 2.5 lb/100 sq ft over 2 applications; blue hydrangeas 2.5 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.34, 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 365,951 surveyed acres in Delaware, IA, 52% are moderately acidic (5.5-6.5), 47% are near neutral (6.5-7.3). Mapped soils run from pH 4.2 to 7.9, a spread of 3.7 units across 350 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 21.2% clay and 3.63% 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. 1% of mapped components carry free carbonate (lime already in the ground).

Delaware against the rest of Iowa

pH 6.34 is right at the Iowa median of 6.36. 40 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: Scott (6.33), Tama (6.33), Carroll (6.34), Clinton (6.34), Des Moines (6.34), Linn (6.34), Benton (6.35), Black Hawk (6.35).

The range in Iowa runs from Van Buren at 6.02 to Monona at 7.11; Delaware sits 29% of the way up.