Soil pH in Washington, CO: Lime or Sulfur?

Typical topsoil pH in Washington, CO

Typical topsoil in Washington, CO is pH 7.14, just outside the 6-7 range for vegetable garden. Test first; it may need nothing.

What Washington needs, by plant

• Just outside, test first: lawn (cool-season grass) (off by 0.1), vegetable garden (off by 0.1), roses (off by 0.1).
• Sulfur: tomatoes 1.4 lb/100 sq ft; potatoes 3.7 lb/100 sq ft over 2 applications; strawberries 2.5 lb/100 sq ft over 2 applications; blueberries 4.8 lb/100 sq ft over 3 applications; azaleas and rhododendrons 4.4 lb/100 sq ft over 3 applications; blue hydrangeas 4.4 lb/100 sq ft over 3 applications; pink hydrangeas 2.1 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 7.14, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, roses.

How mixed the soil is

Of the 1,539,365 surveyed acres in Washington, CO, 82% are near neutral (6.5-7.3), 17% are alkaline (above 7.3), 1% are moderately acidic (5.5-6.5). Mapped soils run from pH 6.3 to 8.2, a spread of 1.9 units across 176 soil components. 82% 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 16.1% clay and 1.66% 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. 21% of mapped components carry free carbonate (lime already in the ground).

Washington against the rest of Colorado

pH 7.14 is right at the Colorado median of 7.17. 28 of 63 Colorado counties have more acidic topsoil. Nationally it is more alkaline than the US county median of 6.05.

Closest in pH within the state: Garfield (7.09), Yuma (7.09), Fremont (7.1), Morgan (7.13), Chaffee (7.16), Phillips (7.17), Sedgwick (7.17), Huerfano (7.18).

The range in Colorado runs from San Juan at 5.53 to Alamosa at 8.28; Washington sits 59% of the way up.