County soil summary
Soil types in Honolulu County, Hawaii
The most widespread soils are Helemano, Wahiawa and Waikane; the most common drainage class is well drained (83% of the land), and typical topsoil pH is 5.8.
- Well or moderately well drained
- 89% of land · state 87%
- Typical topsoil pH
- 5.8 moderately acidic · state 6.0
- Septic fields very limited
- 86% of land · state 93%
- Subject to flooding
- 16% of land, any frequency · state 7%
Most common soils in Honolulu County
Share of mapped land
A county is a patchwork of many soils. These 8 cover 48% of the mapped land; 44 named soil series are mapped here in all.
| Soil | Share of land | Drainage | Topsoil pH |
|---|---|---|---|
| Rough mountainous landGeneral soil group, not a named series | 14.8% | — | — |
| Helemano | 6.6% | Well drained | 6.5 |
| Rock outcropLand type, not a soil series | 6.5% | — | — |
| Wahiawa | 5.8% | Well drained | 5.6 |
| Rock landGeneral soil group, not a named series | 5.4% | — | — |
| Fill land, mixedGeneral soil group, not a named series | 3.2% | — | — |
| Waikane | 3.0% | Well drained | 4.8 |
| Iolekaa | 2.9% | Well drained | 5.0 |
What this means
What the soils in Honolulu County mean for gardens, lawns and septic systems
For your garden
Typical topsoil in Honolulu County is moderately acidic: pH 5.8 (most land between 4.3 and 7.0). Many vegetables grow well here, and some gardens benefit from a little lime. Test before adding any.
Clayey topsoil covers 58% of the land. Clay holds water and nutrients but drains slowly and compacts if worked wet: add compost, avoid tilling soggy soil and consider raised beds. The most common surface texture is silty clay (41% of the land).
89% of the land is moderately well to excessively drained, which suits most garden plants.
For your lawn and yard
Most land is in hydrologic groups B and C, where rain soaks in at a moderate pace.
For a septic system
For conventional septic absorption fields, NRCS rates 86% of the land in Honolulu County very limited, 13% somewhat limited and 0% not limited.
Statewide, 93% of the land is very limited, so Honolulu County is less restrictive than typical.
Where the soil is very limited (slow permeability, a high water table, flooding, shallow bedrock or steep slopes), alternative systems such as mound or sand-filter designs are common and cost more.
Flooding is mapped on 16% of the land (4% occasional, 2% frequent).
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Drainage
How long the soil stays wet
The most common drainage class is well drained (83%). 89% of the land is moderately well drained or better, compared with 87% across Hawaii.
Show as a table
| Category | Honolulu County | Hawaii |
|---|---|---|
| Excessively drained | 4.3% | 13.2% |
| Somewhat excessively drained | 0.0% | 3.1% |
| Well drained | 83.0% | 65.8% |
| Moderately well drained | 1.8% | 4.6% |
| Somewhat poorly drained | 0.0% | 0.6% |
| Poorly drained | 2.6% | 1.9% |
| Very poorly drained | 1.0% | 0.9% |
| Not rated | 7.4% | 9.8% |
Septic absorption fields
NRCS rating for conventional drain fields
The rating looks at the soil from 24 to 60 inches deep: permeability, depth to a seasonal water table or bedrock, flooding and slope. “Very limited” means at least one feature is unfavorable enough that a conventional field is hard to make work.
Show as a table
| Category | Honolulu County | Hawaii |
|---|---|---|
| Not limited | 0.0% | 0.2% |
| Somewhat limited | 13.3% | 5.1% |
| Very limited | 85.8% | 93.1% |
| Not rated | 0.9% | 1.6% |
Rain, runoff and water table
Hydrologic soil group, flooding, seasonal water table
Hydrologic soil group
How fast rain soaks in when the soil is already wet. Group A soaks in fastest, D slowest.
Show as a table
| Category | Honolulu County | Hawaii |
|---|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 15.9% | 29.2% |
| B: moderate infiltration | 37.9% | 18.3% |
| C: slow infiltration | 31.8% | 30.0% |
| D: very slow infiltration (clayey, shallow or wet) | 9.3% | 18.6% |
| A/D: D as is, A if drained | 0.2% | 0.2% |
| B/D: D as is, B if drained | 0.2% | 0.7% |
| C/D: D as is, C if drained | 0.4% | 1.0% |
| Not rated | 4.4% | 2.0% |
Flooding
Show as a table
| Category | Honolulu County | Hawaii |
|---|---|---|
| No flooding | 79.6% | 38.2% |
| Rare or very rare | 10.0% | 2.5% |
| Occasional | 4.0% | 3.6% |
| Frequent or very frequent | 1.7% | 0.6% |
| Not reported | 4.6% | 55.1% |
Seasonal high water table
Show as a table
| Category | Honolulu County | Hawaii |
|---|---|---|
| Within 18 inches at some time of year | 1.1% | 4.0% |
| 18 inches to 3.3 feet | 0.9% | 0.2% |
| Deeper than 3.3 feet or none reported | 93.5% | 40.8% |
| Not reported | 4.6% | 55.1% |
Topsoil pH and texture
First mineral layer of each soil
Typical topsoil pH is 5.8 (moderately acidic); 80% of rated land falls between 4.3 and 7.0. Median topsoil organic matter is 3.5%.
Show as a table
| Category | Honolulu County | Hawaii |
|---|---|---|
| Strongly acidic (below 5.5) | 32.9% | 26.3% |
| Moderately to slightly acidic (5.5–6.4) | 18.5% | 20.5% |
| Near neutral (6.5–7.3) | 36.2% | 29.3% |
| Alkaline (7.4 and up) | 1.3% | 1.7% |
| Not reported | 11.1% | 22.3% |
Texture
Show as a table
| Category | Honolulu County | Hawaii |
|---|---|---|
| Sandy | 1.7% | 6.9% |
| Loamy (loam, silt loam and similar) | 39.4% | 59.0% |
| Clayey (40%+ clay) | 57.7% | 13.8% |
| Organic (muck or peat) | 0.3% | 1.6% |
| Not reported (rock, urban land, etc.) | 0.9% | 18.7% |
Sources & data dates
- Source
- USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
- Data date
- SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
- Scope
- Honolulu County, Hawaii (FIPS 15003): 381,280 acres of mapped land, 14,020 acres of open water excluded. State comparisons pool all mapped land in Hawaii.
- Method
- Shares are by mapped land area: each map unit’s acres in the county times each soil component’s percentage. Open water is excluded. Topsoil values use the first mineral horizon of each component. Full methodology.