Soil pH in Madison, ID: Lime or Sulfur?

Typical topsoil pH in Madison, ID

Typical topsoil in Madison, ID is pH 7.37 and calcareous, so sulfur won't lower it for long. For vegetable garden, choose alkaline-tolerant varieties and add compost rather than fighting the soil.

What Madison needs, by plant

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

What to do next

If your test confirms pH near 7.37, consider raised beds for anything acid-loving; with 39% of soils here carrying free lime, sulfur will not hold.

How mixed the soil is

Of the 279,752 surveyed acres in Madison, ID, 59% are alkaline (above 7.3), 37% are near neutral (6.5-7.3), 4% are moderately acidic (5.5-6.5). Mapped soils run from pH 5.5 to 8.2, a spread of 2.7 units across 120 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 15.8% clay and 3.11% 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. 39% of mapped components carry free carbonate (lime already in the ground), enough that sulfur gets neutralised before it does much.

Madison against the rest of Idaho

pH 7.37 is 0.36 above the Idaho median of 7.01. 35 of 44 Idaho counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Lemhi (7.29), Minidoka (7.34), Payette (7.36), Custer (7.37), Oneida (7.49), Canyon (7.57), Power (7.57), Bingham (7.59).

The range in Idaho runs from Valley at 6.04 to Jefferson at 8.06; Madison sits 66% of the way up.