Soil pH in Franklin, ID: Lime or Sulfur?

Typical topsoil pH in Franklin, ID

Typical topsoil in Franklin, ID is pH 7.26, too alkaline for vegetable garden. Expect roughly 1.8 lb of sulfur per 100 sq ft, but only after a soil test confirms it.

What Franklin needs, by plant

• Sulfur: lawn (cool-season grass) 1.8 lb/100 sq ft; vegetable garden 1.8 lb/100 sq ft; tomatoes 1.8 lb/100 sq ft; potatoes 4.1 lb/100 sq ft over 3 applications; strawberries 3 lb/100 sq ft over 2 applications; roses 1.8 lb/100 sq ft; blueberries 5.3 lb/100 sq ft over 3 applications; azaleas and rhododendrons 4.6 lb/100 sq ft over 3 applications; blue hydrangeas 4.6 lb/100 sq ft over 3 applications; pink hydrangeas 2.3 lb/100 sq ft over 2 applications.

What to do next

If your test confirms pH near 7.26, work in about 18 lb of elemental sulfur per 1,000 sq ft of vegetable bed.

How mixed the soil is

Of the 321,022 surveyed acres in Franklin, ID, 46% are near neutral (6.5-7.3), 44% are alkaline (above 7.3), 10% are moderately acidic (5.5-6.5). Mapped soils run from pH 5.2 to 10.1, a spread of 4.9 units across 736 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 19.7% clay and 3.04% 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. 28% of mapped components carry free carbonate (lime already in the ground).

Franklin against the rest of Idaho

pH 7.26 is 0.25 above the Idaho median of 7.01. 28 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: Ada (7.18), Bear Lake (7.18), Clark (7.19), Elmore (7.26), Twin Falls (7.27), Jerome (7.29), Lemhi (7.29), Minidoka (7.34).

The range in Idaho runs from Valley at 6.04 to Jefferson at 8.06; Franklin sits 60% of the way up.