Soil pH in Benton, OR: Lime or Sulfur?

Typical topsoil pH in Benton, OR

Typical topsoil in Benton, OR is pH 5.47, too acidic for vegetable garden. Expect roughly 11.5 lb of lime per 100 sq ft, but only after a soil test confirms it.

What Benton 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) 11.5 lb/100 sq ft over 3 applications; vegetable garden 11.5 lb/100 sq ft over 3 applications; tomatoes 11.5 lb/100 sq ft over 3 applications; roses 11.5 lb/100 sq ft over 3 applications; pink hydrangeas 9.2 lb/100 sq ft over 2 applications.

What to do next

If your test confirms pH near 5.47, spread about 115 lb of ground limestone per 1,000 sq ft of vegetable bed in 3 doses, ideally in fall.

How mixed the soil is

Of the 383,038 surveyed acres in Benton, OR, 61% are moderately acidic (5.5-6.5), 39% are strongly acidic (below 5.5). Mapped soils run from pH 4.6 to 6.7, a spread of 2.1 units across 401 soil components. 61% 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 26.1% clay and 6.45% organic matter, which this site treats as clay. At 6.45% 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.

Benton against the rest of Oregon

pH 5.47 is 0.83 below the Oregon median of 6.3. 5 of 36 Oregon counties have more acidic topsoil. Nationally it is more acidic than the US county median of 6.05.

Closest in pH within the state: Lincoln (4.99), Tillamook (5), Coos (5.22), Curry (5.36), Polk (5.52), Lane (5.53), Yamhill (5.55), Columbia (5.57).

The range in Oregon runs from Clatsop at 4.89 to Malheur at 7.9; Benton sits 19% of the way up.