Soil pH in Audubon, IA: Lime or Sulfur?

Typical topsoil pH in Audubon, IA

Typical topsoil in Audubon, IA is pH 6.09, already right for vegetable garden (6-7). Test before adding anything.

What Audubon needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, strawberries, roses, pink hydrangeas.
• Just outside, test first: tomatoes (off by 0.1), potatoes (off by 0.1), azaleas and rhododendrons (off by 0.1).
• Sulfur: blueberries 3.7 lb/100 sq ft over 2 applications; blue hydrangeas 2.7 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.09, 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 282,550 surveyed acres in Audubon, IA, 95% are moderately acidic (5.5-6.5), 4% are near neutral (6.5-7.3). Mapped soils run from pH 5.6 to 7.9, a spread of 2.3 units across 191 soil components. 95% 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 30.8% clay and 3.22% 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. 1% of mapped components carry free carbonate (lime already in the ground).

Audubon against the rest of Iowa

pH 6.09 is 0.27 below the Iowa median of 6.36. 2 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: Van Buren (6.02), Ida (6.07), Shelby (6.11), Lee (6.12), Montgomery (6.12), Cass (6.13).

The range in Iowa runs from Van Buren at 6.02 to Monona at 7.11; Audubon sits 6% of the way up.