Soil pH in Humboldt, IA: Lime or Sulfur?

Typical topsoil pH in Humboldt, IA

Typical topsoil in Humboldt, IA is pH 6.79, already right for vegetable garden (6-7). Test before adding anything.

What Humboldt needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, roses.
• Beds or pots instead: potatoes, strawberries, blueberries, azaleas and rhododendrons, blue hydrangeas, pink hydrangeas.

What to do next

If your test lands near 6.79, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, roses.

How mixed the soil is

Of the 276,166 surveyed acres in Humboldt, IA, 34% are near neutral (6.5-7.3), 33% are moderately acidic (5.5-6.5), 32% are alkaline (above 7.3). Mapped soils run from pH 5.9 to 8.2, a spread of 2.3 units across 189 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 29.5% clay and 6.03% organic matter, which this site treats as clay. At 6.03% 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. 35% of mapped components carry free carbonate (lime already in the ground), enough that sulfur gets neutralised before it does much.

Humboldt against the rest of Iowa

pH 6.79 is 0.43 above the Iowa median of 6.36. 94 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: Pocahontas (6.73), Hamilton (6.74), Boone (6.76), Kossuth (6.78), Hancock (6.8), Woodbury (6.89), Harrison (6.91), Monona (7.11).

The range in Iowa runs from Van Buren at 6.02 to Monona at 7.11; Humboldt sits 71% of the way up.