Soil pH in Spokane, WA: Lime or Sulfur?

Typical topsoil pH in Spokane, WA

Typical topsoil in Spokane, WA is pH 6.41, already right for vegetable garden (6-7). Test before adding anything.

What Spokane needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.
• Sulfur: potatoes 2.1 lb/100 sq ft over 2 applications; blueberries 3.2 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 6.41, 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 0 surveyed acres in Spokane, WA, 58% are near neutral (6.5-7.3), 39% are moderately acidic (5.5-6.5), 2% are strongly acidic (below 5.5), 2% are alkaline (above 7.3). Mapped soils run from pH 5.1 to 8.8, a spread of 3.7 units across 1,576 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 11.8% clay and 3.08% 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. 1% of mapped components carry free carbonate (lime already in the ground).

Spokane against the rest of Washington

pH 6.41 is right at the Washington median of 6.41. 19 of 39 Washington counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Snohomish (5.68), Cowlitz (5.74), Thurston (5.76), Skamania (5.86), Okanogan (6.45), Kittitas (6.47), Pend Oreille (6.49), Chelan (6.5).

The range in Washington runs from Grays Harbor at 4.93 to Adams at 7.45; Spokane sits 59% of the way up.