Soil pH in Lewis and Clark, MT: Lime or Sulfur?

Typical topsoil pH in Lewis and Clark, MT

Typical topsoil in Lewis and Clark, MT is pH 6.78, already right for vegetable garden (6-7). Test before adding anything.

What Lewis and Clark needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, roses.
• Sulfur: potatoes 3 lb/100 sq ft over 2 applications; strawberries 1.8 lb/100 sq ft; blueberries 4.1 lb/100 sq ft over 3 applications; azaleas and rhododendrons 3.5 lb/100 sq ft over 2 applications; blue hydrangeas 3.5 lb/100 sq ft over 2 applications; pink hydrangeas 1.2 lb/100 sq ft.

What to do next

If your test lands near 6.78, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, roses.

How mixed the soil is

Of the 1,840,346 surveyed acres in Lewis and Clark, MT, 45% are near neutral (6.5-7.3), 34% are moderately acidic (5.5-6.5), 21% are alkaline (above 7.3). Mapped soils run from pH 5.3 to 8.7, a spread of 3.4 units across 1,101 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 18.7% clay and 2.54% 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. 18% of mapped components carry free carbonate (lime already in the ground).

Lewis and Clark against the rest of Montana

pH 6.78 is 0.52 below the Montana median of 7.3. 14 of 56 Montana counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Madison (6.46), Powell (6.46), Meagher (6.47), Lake (6.69), Beaverhead (6.79), Gallatin (6.85), Jefferson (6.95), Glacier (7.15).

The range in Montana runs from Flathead at 6.02 to Wheatland at 7.77; Lewis and Clark sits 43% of the way up.