Soil pH in Thurston, WA: Lime or Sulfur?

Typical topsoil pH in Thurston, WA

Typical topsoil in Thurston, WA is pH 5.76, just outside the 6-7 range for vegetable garden. Test first; it may need nothing.

What Thurston needs, by plant

• Already in range: potatoes, strawberries, azaleas and rhododendrons.
• Just outside, test first: lawn (cool-season grass) (off by 0.2), vegetable garden (off by 0.2), roses (off by 0.2), pink hydrangeas (off by 0.2).
• Lime: tomatoes 8 lb/100 sq ft over 2 applications.
• Sulfur: blueberries 2.7 lb/100 sq ft over 2 applications; blue hydrangeas 1.7 lb/100 sq ft.

What to do next

If your test lands near 5.76, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, potatoes, strawberries, roses, azaleas and rhododendrons, pink hydrangeas.

How mixed the soil is

Of the 456,800 surveyed acres in Thurston, WA, 80% are moderately acidic (5.5-6.5), 18% are strongly acidic (below 5.5), 3% are near neutral (6.5-7.3). Mapped soils run from pH 4.3 to 6.7, a spread of 2.4 units across 206 soil components. 80% 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 14.4% clay and 7.14% organic matter, which this site treats as clay. At 7.14% organic matter the soil buffers like a heavier one, which pushes it into the clay bracket. Moving it one pH unit takes about 11.5 lb of lime or 3.4 lb of sulfur per 100 sq ft. None of the mapped components carry free carbonate.

Thurston against the rest of Washington

pH 5.76 is 0.65 below the Washington median of 6.41. 17 of 39 Washington counties have more acidic topsoil. Nationally it is more acidic than the US county median of 6.05.

Closest in pH within the state: Clark (5.62), Island (5.67), Snohomish (5.68), Cowlitz (5.74), Skamania (5.86), Spokane (6.41), Okanogan (6.45), Kittitas (6.47).

The range in Washington runs from Grays Harbor at 4.93 to Adams at 7.45; Thurston sits 33% of the way up.