Soil pH in Idaho, ID: Lime or Sulfur?

Typical topsoil pH in Idaho, ID

Typical topsoil in Idaho, ID is pH 6.46, already right for vegetable garden (6-7). Test before adding anything.

What Idaho needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.
• Sulfur: potatoes 2.3 lb/100 sq ft over 2 applications; blueberries 3.5 lb/100 sq ft over 2 applications; azaleas and rhododendrons 2.8 lb/100 sq ft over 2 applications; blue hydrangeas 2.8 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.46, 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 1,758,654 surveyed acres in Idaho, ID, 72% are near neutral (6.5-7.3), 26% are moderately acidic (5.5-6.5), 2% are strongly acidic (below 5.5). Mapped soils run from pH 5 to 7.5, a spread of 2.5 units across 674 soil components. 72% 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 18.1% clay and 3.61% 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. None of the mapped components carry free carbonate.

Idaho against the rest of Idaho

pH 6.46 is 0.55 below the Idaho median of 7.01. 9 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: Shoshone (6.32), Bonner (6.38), Fremont (6.42), Kootenai (6.44), Lewis (6.46), Benewah (6.49), Camas (6.49), Caribou (6.53).

The range in Idaho runs from Valley at 6.04 to Jefferson at 8.06; Idaho sits 21% of the way up.