Soil pH in Washington, RI: Lime or Sulfur?

Typical topsoil pH in Washington, RI

Typical topsoil in Washington, RI is pH 5.08, too acidic for vegetable garden. Expect roughly 9.8 lb of lime per 100 sq ft, but only after a soil test confirms it.

What Washington needs, by plant

• Already in range: potatoes, blueberries, azaleas and rhododendrons, blue hydrangeas.
• Lime: lawn (cool-season grass) 9.8 lb/100 sq ft over 2 applications; vegetable garden 9.8 lb/100 sq ft over 2 applications; tomatoes 9.8 lb/100 sq ft over 2 applications; strawberries 6.3 lb/100 sq ft over 2 applications; roses 9.8 lb/100 sq ft over 2 applications; pink hydrangeas 8.4 lb/100 sq ft over 2 applications.

What to do next

If your test confirms pH near 5.08, spread about 98 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 201,107 surveyed acres in Washington, RI, 80% are strongly acidic (below 5.5), 17% are moderately acidic (5.5-6.5), 1% are alkaline (above 7.3), 1% are near neutral (6.5-7.3). Mapped soils run from pH 3.8 to 8, a spread of 4.2 units across 647 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 5.7% clay and 5.78% organic matter, which this site treats as loam. At 5.78% 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. 1% of mapped components carry free carbonate (lime already in the ground).

Washington against the rest of Rhode Island

pH 5.08 is right at the Rhode Island median of 5.08. 2 of 5 Rhode Island counties have more acidic topsoil. Nationally it is more acidic than the US county median of 6.05.

Closest in pH within the state: Providence (4.97), Kent (5), Bristol (5.21), Newport (5.21).

The range in Rhode Island runs from Providence at 4.97 to Newport at 5.21; Washington sits 46% of the way up.