Soil pH in Denver, CO: Lime or Sulfur?

Typical topsoil pH in Denver, CO

Typical topsoil in Denver, CO is pH 7.24, just outside the 6-7 range for vegetable garden. Test first; it may need nothing.

What Denver needs, by plant

• Just outside, test first: lawn (cool-season grass) (off by 0.2), vegetable garden (off by 0.2), roses (off by 0.2).
• Sulfur: tomatoes 1.6 lb/100 sq ft; potatoes 3.9 lb/100 sq ft over 2 applications; strawberries 2.8 lb/100 sq ft over 2 applications; blueberries 5.1 lb/100 sq ft over 3 applications; azaleas and rhododendrons 4.6 lb/100 sq ft over 3 applications; blue hydrangeas 4.6 lb/100 sq ft over 3 applications; pink hydrangeas 2.3 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 7.24, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, roses.

How mixed the soil is

Of the 63,807 surveyed acres in Denver, CO, 60% are near neutral (6.5-7.3), 38% are alkaline (above 7.3), 2% are moderately acidic (5.5-6.5). Mapped soils run from pH 5.6 to 8.2, a spread of 2.6 units across 347 soil components. 60% 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 19.5% clay and 1.45% 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. 18% of mapped components carry free carbonate (lime already in the ground).

Denver against the rest of Colorado

pH 7.24 is 0.07 above the Colorado median of 7.17. 36 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: Huerfano (7.18), Costilla (7.19), Logan (7.2), Arapahoe (7.22), Adams (7.25), Broomfield (7.29), Weld (7.29), Kit Carson (7.33).

The range in Colorado runs from San Juan at 5.53 to Alamosa at 8.28; Denver sits 62% of the way up.