State soil summary
Soil types in Washington
The most widespread soil series in Washington are Ritzville, Shano, Alderwood. Pick a county below, or enter a ZIP code for the county you live in.
- Well or moderately well drained
- 82% of mapped land
- Typical topsoil pH
- 6.5 slightly acidic · most land 4.8–7.3
- Septic fields very limited
- 81% <1% not limited
- Subject to flooding
- 4% of land, any frequency
Washington counties
11 county reports, by population
| County | Most common soil | Well drained | Topsoil pH | Septic very limited |
|---|---|---|---|---|
| King County | Alderwood | 84% | 5.6 | 93% |
| Pierce County | Kapowsin | 79% | 5.5 | 93% |
| Snohomish County | Tokul | 79% | 5.8 | 92% |
| Spokane County | Naff | 85% | 6.5 | 90% |
| Clark County | Cinebar | 90% | 5.6 | 85% |
| Thurston County | Spanaway | 85% | 5.8 | 92% |
| Kitsap County | Alderwood | 87% | 5.6 | 92% |
| Yakima County | Warden | 86% | 7.0 | 73% |
| Whatcom County | Doubtful | 74% | 5.6 | 90% |
| Benton County | Ritzville | 98% | 7.5 | 53% |
| Skagit County | Vanzandt | 77% | 5.6 | 95% |
What this means
What Washington soils mean for gardens, lawns and septic systems
For gardens
Typical topsoil in Washington is slightly acidic: pH 6.5 (most land between 4.8 and 7.3), the range most vegetables, flowers and lawn grasses prefer.
Loamy topsoil (loam, silt loam and similar) covers 78% of the land: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (21% of the land).
82% of the land is moderately well to excessively drained, which suits most garden plants.
For lawns and yards
Most land is in hydrologic groups B and C, where rain soaks in at a moderate pace.
For septic systems
For conventional septic absorption fields, NRCS rates 81% of the land in Washington very limited, 9% somewhat limited and <1% not limited (9% not rated, such as urban land, pits or water).
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.
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Statewide mix
Share of all mapped land
Drainage
Show as a table
| Category | Share of land |
|---|---|
| Excessively drained | 2.1% |
| Somewhat excessively drained | 5.7% |
| Well drained | 65.7% |
| Moderately well drained | 8.7% |
| Somewhat poorly drained | 2.4% |
| Poorly drained | 2.3% |
| Very poorly drained | 0.7% |
| Not rated | 12.4% |
Septic absorption fields
Show as a table
| Category | Share of land |
|---|---|
| Not limited | 0.6% |
| Somewhat limited | 9.4% |
| Very limited | 81.4% |
| Not rated | 8.6% |
Topsoil pH
Show as a table
| Category | Share of land |
|---|---|
| Strongly acidic (below 5.5) | 17.7% |
| Moderately to slightly acidic (5.5–6.4) | 22.4% |
| Near neutral (6.5–7.3) | 37.6% |
| Alkaline (7.4 and up) | 8.2% |
| Not reported | 14.1% |
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
- Washington: 41,437,604 acres of mapped land in 39 counties, pooled (not an average of county figures).
- 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.