Soil pH in Durham, NC: Lime or Sulfur?

Typical topsoil pH in Durham, NC

Typical topsoil in Durham, NC is pH 5.55, too acidic for vegetable garden. Expect roughly 7 lb of lime per 100 sq ft, but only after a soil test confirms it.

What Durham needs, by plant

• Already in range: potatoes, strawberries, azaleas and rhododendrons.
• Just outside, test first: blueberries (off by 0), blue hydrangeas (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 4.9 lb/100 sq ft.

What to do next

If your test confirms pH near 5.55, 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 170,570 surveyed acres in Durham, NC, 65% are moderately acidic (5.5-6.5), 34% are strongly acidic (below 5.5), 1% are near neutral (6.5-7.3). Mapped soils run from pH 4.5 to 7, a spread of 2.5 units across 171 soil components. 65% 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 15% clay and 1.43% 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.

Durham against the rest of North Carolina

pH 5.55 is 0.39 above the North Carolina median of 5.16. 78 of 100 North Carolina counties have more acidic topsoil. Nationally it is more acidic than the US county median of 6.05.

Closest in pH within the state: Orange (5.5), Alexander (5.52), Davidson (5.52), Caswell (5.54), Stokes (5.55), Surry (5.56), Wake (5.56), Franklin (5.57).

The range in North Carolina runs from Swain at 4.56 to Davie at 5.9; Durham sits 74% of the way up.