Soil pH in Coos, OR: Lime or Sulfur?

Typical topsoil pH in Coos, OR

Typical topsoil in Coos, OR is pH 5.22, too acidic for vegetable garden. Expect roughly 15 lb of lime per 100 sq ft, but only after a soil test confirms it.

What Coos needs, by plant

• Already in range: potatoes, blueberries, azaleas and rhododendrons, blue hydrangeas.
• Lime: lawn (cool-season grass) 15 lb/100 sq ft over 3 applications; vegetable garden 15 lb/100 sq ft over 3 applications; tomatoes 15 lb/100 sq ft over 3 applications; strawberries 9.2 lb/100 sq ft over 2 applications; roses 15 lb/100 sq ft over 3 applications; pink hydrangeas 11.5 lb/100 sq ft over 3 applications.

What to do next

If your test confirms pH near 5.22, spread about 150 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 785,063 surveyed acres in Coos, OR, 78% are strongly acidic (below 5.5), 20% are moderately acidic (5.5-6.5), 2% are near neutral (6.5-7.3). Mapped soils run from pH 4.3 to 7.2, a spread of 2.9 units across 250 soil components. 78% 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 20% clay and 5.58% organic matter, which this site treats as clay. At 5.58% 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.

Coos against the rest of Oregon

pH 5.22 is 1.08 below the Oregon median of 6.3. 3 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: Clatsop (4.89), Lincoln (4.99), Tillamook (5), Curry (5.36), Benton (5.47), Polk (5.52), Lane (5.53).

The range in Oregon runs from Clatsop at 4.89 to Malheur at 7.9; Coos sits 11% of the way up.