Soil pH in Fairfax City, VA: Lime or Sulfur?

Typical topsoil pH in Fairfax City, VA

Typical topsoil in Fairfax City, VA is pH 6.28, already right for vegetable garden (6-7). Test before adding anything.

What Fairfax City needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.
• Sulfur: potatoes 1.8 lb/100 sq ft; blueberries 3 lb/100 sq ft over 2 applications; azaleas and rhododendrons 2.3 lb/100 sq ft over 2 applications; blue hydrangeas 2.3 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.28, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, strawberries, roses, pink hydrangeas.

How mixed the soil is

Of the 2,286 surveyed acres in Fairfax City, VA, 46% are alkaline (above 7.3), 46% are strongly acidic (below 5.5), 4% are near neutral (6.5-7.3), 4% are moderately acidic (5.5-6.5). Mapped soils run from pH 4.5 to 7.5, a spread of 3 units across 49 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 18.7% 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.

Fairfax City against the rest of Virginia

pH 6.28 is 1.04 above the Virginia median of 5.24. 124 of 127 Virginia counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Bedford City (5.78), Wise (5.82), South Boston City (5.82), Danville City (5.95), Falls Church City (6.32), Poquoson City (6.36).

The range in Virginia runs from Newport News City at 4.76 to Poquoson City at 6.36; Fairfax City sits 95% of the way up.