Soil pH in Washington, OK: Lime or Sulfur?

Typical topsoil pH in Washington, OK

Typical topsoil in Washington, OK is pH 6.19, already right for vegetable garden (6-7). Test before adding anything.

What Washington needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, strawberries, roses, pink hydrangeas.
• Just outside, test first: tomatoes (off by 0), potatoes (off by 0.2), azaleas and rhododendrons (off by 0.2).
• Sulfur: blueberries 2.8 lb/100 sq ft over 2 applications; blue hydrangeas 2.1 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.19, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, potatoes, strawberries, roses, azaleas and rhododendrons, pink hydrangeas.

How mixed the soil is

Of the 257,060 surveyed acres in Washington, OK, 56% are moderately acidic (5.5-6.5), 43% are near neutral (6.5-7.3), 1% are strongly acidic (below 5.5). Mapped soils run from pH 5.2 to 7.3, a spread of 2.1 units across 118 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 24.8% clay and 2.44% 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. None of the mapped components carry free carbonate.

Washington against the rest of Oklahoma

pH 6.19 is 0.36 below the Oklahoma median of 6.55. 25 of 77 Oklahoma counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Tulsa (6.12), Nowata (6.15), Okfuskee (6.15), Choctaw (6.19), Pontotoc (6.27), Seminole (6.33), Osage (6.34), Oklahoma (6.35).

The range in Oklahoma runs from Adair at 5.12 to Beaver at 7.65; Washington sits 42% of the way up.