Soil pH in Knox, IL: Lime or Sulfur?

Typical topsoil pH in Knox, IL

Typical topsoil in Knox, IL is pH 6.33, already right for vegetable garden (6-7). Test before adding anything.

What Knox 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 6.33, 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 447,491 surveyed acres in Knox, IL, 55% are moderately acidic (5.5-6.5), 44% are near neutral (6.5-7.3), 1% are alkaline (above 7.3). Mapped soils run from pH 5.8 to 7.9, a spread of 2.1 units across 187 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 23% clay and 2.82% 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. 5% of mapped components carry free carbonate (lime already in the ground).

Knox against the rest of Illinois

pH 6.33 is 0.07 below the Illinois median of 6.4. 29 of 102 Illinois counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Gallatin (6.3), Morgan (6.3), Wabash (6.31), Clark (6.33), Perry (6.33), Washington (6.33), Logan (6.34), Marion (6.34).

The range in Illinois runs from Pope at 5.5 to Grundy at 6.75; Knox sits 66% of the way up.