Soil pH in Boise, ID: Lime or Sulfur?

Typical topsoil pH in Boise, ID

Typical topsoil in Boise, ID is pH 6.25, already right for vegetable garden (6-7). Test before adding anything.

What Boise needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.
• Sulfur: potatoes 1 lb/100 sq ft; blueberries 1.6 lb/100 sq ft; azaleas and rhododendrons 1.2 lb/100 sq ft; blue hydrangeas 1.2 lb/100 sq ft.

What to do next

If your test lands near 6.25, 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 110,450 surveyed acres in Boise, ID, 45% are moderately acidic (5.5-6.5), 45% are near neutral (6.5-7.3), 11% are strongly acidic (below 5.5). Mapped soils run from pH 5.3 to 6.7, a spread of 1.4 units across 66 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 7% clay and 2.75% organic matter, which this site treats as sandy. Moving it one pH unit takes about 3 lb of lime or 1.2 lb of sulfur per 100 sq ft. None of the mapped components carry free carbonate.

Boise against the rest of Idaho

pH 6.25 is 0.76 below the Idaho median of 7.01. 2 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: Valley (6.04), Latah (6.18), Boundary (6.29), Clearwater (6.32), Shoshone (6.32), Bonner (6.38).

The range in Idaho runs from Valley at 6.04 to Jefferson at 8.06; Boise sits 10% of the way up.