County soil summary
Soil types in Suffolk County, New York
The most widespread soils are Riverhead, Plymouth and Haven; the most common drainage class is well drained (42% of the land), and typical topsoil pH is 5.0.
- Well or moderately well drained
- 79% of land · state 63%
- Typical topsoil pH
- 5.0 very strongly acidic · state 5.5
- Septic fields very limited
- 76% of land · state 84%
- Subject to flooding
- 6% of land, any frequency · state 4%
Most common soils in Suffolk County
Share of mapped land
A county is a patchwork of many soils. These 8 cover 79% of the mapped land; 36 named soil series are mapped here in all.
| Soil | Share of land | Drainage | Topsoil pH |
|---|---|---|---|
| Riverhead | 21.3% | Well drained | 5.0 |
| Plymouth | 18.6% | Excessively drained | 4.4 |
| Haven | 14.8% | Well drained | 5.3 |
| Carver | 9.2% | Excessively drained | 4.0 |
| Cut and fillGeneral soil group, not a named series | 5.4% | — | — |
| MontaukGeneral soil group, not a named series | 4.0% | — | — |
| BridgehamptonGeneral soil group, not a named series | 2.9% | — | — |
| Tidal marshGeneral soil group, not a named series | 2.6% | — | — |
What this means
What the soils in Suffolk County mean for gardens, lawns and septic systems
For your garden
Typical topsoil in Suffolk County is very strongly acidic: pH 5.0 (most land between 4.0 and 5.3). Most vegetables and lawn grasses do best around 6.0 to 7.0, so lime is often needed; blueberries, azaleas and rhododendrons like it as it is.
Loamy topsoil (loam, silt loam and similar) covers 43% of the land: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is sandy loam (22% of the land).
31% of the land is excessively or somewhat excessively drained: water moves through fast, so gardens need more frequent watering in dry spells.
For your lawn and yard
53% of the land is in hydrologic group A, where water soaks in fast. Lawns there dry out quickly; deeper, less frequent watering and organic matter help.
For a septic system
For conventional septic absorption fields, NRCS rates 76% of the land in Suffolk County very limited, 1% somewhat limited and <1% not limited (22% not rated, such as urban land, pits or water).
Statewide, 84% of the land is very limited, so Suffolk 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 6% of the land (0% occasional, 4% 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 (42%). 79% of the land is moderately well drained or better, compared with 63% across New York.
Show as a table
| Category | Suffolk County | New York |
|---|---|---|
| Excessively drained | 30.9% | 2.8% |
| Somewhat excessively drained | 0.0% | 7.9% |
| Well drained | 41.9% | 32.9% |
| Moderately well drained | 6.3% | 19.2% |
| Somewhat poorly drained | 0.4% | 16.6% |
| Poorly drained | 0.8% | 5.4% |
| Very poorly drained | 3.7% | 5.2% |
| Not rated | 16.1% | 10.0% |
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 | Suffolk County | New York |
|---|---|---|
| Not limited | 0.3% | 0.2% |
| Somewhat limited | 1.1% | 3.3% |
| Very limited | 76.3% | 83.5% |
| Not rated | 22.3% | 13.0% |
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 | Suffolk County | New York |
|---|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 52.8% | 10.0% |
| B: moderate infiltration | 17.5% | 12.9% |
| C: slow infiltration | 2.4% | 13.1% |
| D: very slow infiltration (clayey, shallow or wet) | 0.9% | 25.3% |
| A/D: D as is, A if drained | 1.7% | 3.5% |
| B/D: D as is, B if drained | 1.1% | 9.5% |
| C/D: D as is, C if drained | 0.1% | 11.6% |
| Not rated | 23.4% | 14.2% |
Flooding
Show as a table
| Category | Suffolk County | New York |
|---|---|---|
| No flooding | 73.7% | 83.0% |
| Rare or very rare | 2.2% | 0.4% |
| Occasional | 0.0% | 1.3% |
| Frequent or very frequent | 4.2% | 2.1% |
| Not reported | 20.0% | 13.3% |
Seasonal high water table
Show as a table
| Category | Suffolk County | New York |
|---|---|---|
| Within 18 inches at some time of year | 6.0% | 32.8% |
| 18 inches to 3.3 feet | 5.5% | 18.5% |
| Deeper than 3.3 feet or none reported | 76.5% | 42.9% |
| Not reported | 12.1% | 5.8% |
Topsoil pH and texture
First mineral layer of each soil
Typical topsoil pH is 5.0 (very strongly acidic); 80% of rated land falls between 4.0 and 5.3. Median topsoil organic matter is 3%.
Show as a table
| Category | Suffolk County | New York |
|---|---|---|
| Strongly acidic (below 5.5) | 71.0% | 40.7% |
| Moderately to slightly acidic (5.5–6.4) | 5.1% | 29.9% |
| Near neutral (6.5–7.3) | 0.1% | 13.2% |
| Alkaline (7.4 and up) | 0.0% | 0.6% |
| Not reported | 23.8% | 15.6% |
Texture
Show as a table
| Category | Suffolk County | New York |
|---|---|---|
| Sandy | 33.6% | 5.9% |
| Loamy (loam, silt loam and similar) | 42.5% | 76.3% |
| Clayey (40%+ clay) | 0.0% | 0.6% |
| Organic (muck or peat) | 0.8% | 2.8% |
| Not reported (rock, urban land, etc.) | 23.1% | 14.4% |
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
- Suffolk County, New York (FIPS 36103): 580,280 acres of mapped land, 161,281 acres of open water excluded. State comparisons pool all mapped land in New York.
- 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.