Soil pH in Honolulu, HI: Lime or Sulfur?

Typical topsoil pH in Honolulu, HI

Typical topsoil in Honolulu, HI is pH 5.81, just outside the 6-7 range for vegetable garden. Test first; it may need nothing.

What Honolulu needs, by plant

• Already in range: potatoes, strawberries, azaleas and rhododendrons.
• Just outside, test first: lawn (cool-season grass) (off by 0.2), vegetable garden (off by 0.2), roses (off by 0.2), pink hydrangeas (off by 0.2).
• Lime: tomatoes 8 lb/100 sq ft over 2 applications.
• Sulfur: blueberries 2.7 lb/100 sq ft over 2 applications; blue hydrangeas 2 lb/100 sq ft.

What to do next

If your test lands near 5.81, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, potatoes, strawberries, roses, azaleas and rhododendrons, pink hydrangeas.

How mixed the soil is

Of the 339,137 surveyed acres in Honolulu, HI, 41% are near neutral (6.5-7.3), 37% are strongly acidic (below 5.5), 21% are moderately acidic (5.5-6.5), 2% are alkaline (above 7.3). Mapped soils run from pH 4 to 8.2, a spread of 4.2 units across 178 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 46.1% clay and 7.38% organic matter, which this site treats as clay. At 7.38% organic matter the soil buffers like a heavier one, which pushes it into the clay bracket. Moving it one pH unit takes about 11.5 lb of lime or 3.4 lb of sulfur per 100 sq ft. 8% of mapped components carry free carbonate (lime already in the ground).

Honolulu against the rest of Hawaii

pH 5.81 is right at the Hawaii median of 5.83. 1 of 5 Hawaii counties have more acidic topsoil. Nationally it is more acidic than the US county median of 6.05.

Closest in pH within the state: Kauai (5.26), Maui (5.83), Hawaii (6.01), Kalawao (6.6).

The range in Hawaii runs from Kauai at 5.26 to Kalawao at 6.6; Honolulu sits 41% of the way up.