Soil pH in King, WA: Lime or Sulfur?

Typical topsoil pH in King, WA

Typical topsoil in King, WA is pH 5.45, too acidic for vegetable garden. Expect roughly 7 lb of lime per 100 sq ft, but only after a soil test confirms it.

What King needs, by plant

• Already in range: potatoes, blueberries, azaleas and rhododendrons, blue hydrangeas.
• Just outside, test first: strawberries (off by 0).
• Lime: lawn (cool-season grass) 7 lb/100 sq ft over 2 applications; vegetable garden 7 lb/100 sq ft over 2 applications; tomatoes 7 lb/100 sq ft over 2 applications; roses 7 lb/100 sq ft over 2 applications; pink hydrangeas 5.6 lb/100 sq ft over 2 applications.

What to do next

If your test confirms pH near 5.45, spread about 70 lb of ground limestone per 1,000 sq ft of vegetable bed in 2 doses, ideally in fall.

How mixed the soil is

Of the 1,008,197 surveyed acres in King, WA, 55% are moderately acidic (5.5-6.5), 44% are strongly acidic (below 5.5), 2% are near neutral (6.5-7.3). Mapped soils run from pH 4 to 7, a spread of 3 units across 400 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 8.4% clay and 8.5% organic matter, which this site treats as loam. At 8.5% organic matter the soil buffers like a heavier one, which pushes it into the loam bracket. Moving it one pH unit takes about 7 lb of lime or 2.3 lb of sulfur per 100 sq ft. None of the mapped components carry free carbonate.

King against the rest of Washington

pH 5.45 is 0.96 below the Washington median of 6.41. 8 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: Clallam (5.23), Jefferson (5.24), Mason (5.4), Whatcom (5.41), Pierce (5.48), Kitsap (5.49), San Juan (5.56), Skagit (5.58).

The range in Washington runs from Grays Harbor at 4.93 to Adams at 7.45; King sits 21% of the way up.