Soil pH in Hawaii, HI: Lime or Sulfur?

Typical topsoil pH in Hawaii, HI

Typical topsoil in Hawaii, HI is pH 6.01, already right for vegetable garden (6-7). Test before adding anything.

What Hawaii needs, by plant

• Already in range: lawn (cool-season grass), vegetable garden, strawberries, roses, pink hydrangeas.
• Just outside, test first: tomatoes (off by 0.2), potatoes (off by 0), azaleas and rhododendrons (off by 0).
• Sulfur: blueberries 3.4 lb/100 sq ft over 2 applications; blue hydrangeas 2.7 lb/100 sq ft over 2 applications.

What to do next

If your test lands near 6.01, you can skip lime and sulfur for lawn (cool-season grass), vegetable garden, tomatoes, potatoes, strawberries, roses, azaleas and rhododendrons, pink hydrangeas.

How mixed the soil is

Of the 1,907,491 surveyed acres in Hawaii, HI, 36% are near neutral (6.5-7.3), 31% are moderately acidic (5.5-6.5), 31% are strongly acidic (below 5.5), 2% are alkaline (above 7.3). Mapped soils run from pH 3.1 to 7.6, a spread of 4.5 units across 1,290 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 15.6% clay and 13.22% organic matter, which this site treats as clay. At 13.22% 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. 0% of mapped components carry free carbonate (lime already in the ground).

Hawaii against the rest of Hawaii

pH 6.01 is 0.18 above the Hawaii median of 5.83. 3 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), Honolulu (5.81), Maui (5.83), Kalawao (6.6).

The range in Hawaii runs from Kauai at 5.26 to Kalawao at 6.6; Hawaii sits 56% of the way up.