Soil pH in Douglas, CO: Lime or Sulfur?

Typical topsoil pH in Douglas, CO

Typical topsoil in Douglas, CO is pH 6.81, already right for vegetable garden (6-7). Test before adding anything.

What Douglas needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, roses.
• Just outside, test first: tomatoes (off by 0).
• Sulfur: potatoes 3 lb/100 sq ft over 2 applications; strawberries 1.8 lb/100 sq ft; blueberries 4.1 lb/100 sq ft over 3 applications; azaleas and rhododendrons 3.7 lb/100 sq ft over 2 applications; blue hydrangeas 3.7 lb/100 sq ft over 2 applications; pink hydrangeas 1.4 lb/100 sq ft.

What to do next

If your test lands near 6.81, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, roses.

How mixed the soil is

Of the 334,039 surveyed acres in Douglas, CO, 87% are near neutral (6.5-7.3), 7% are moderately acidic (5.5-6.5), 7% are alkaline (above 7.3). Mapped soils run from pH 5 to 7.9, a spread of 2.9 units across 232 soil components. 87% 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 13.8% clay and 2.14% 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. 8% of mapped components carry free carbonate (lime already in the ground).

Douglas against the rest of Colorado

pH 6.81 is 0.36 below the Colorado median of 7.17. 14 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: Larimer (6.6), Jefferson (6.72), Boulder (6.75), Custer (6.75), El Paso (6.81), Archuleta (6.83), La Plata (6.88), Dolores (6.89).

The range in Colorado runs from San Juan at 5.53 to Alamosa at 8.28; Douglas sits 47% of the way up.