County soil summary
Soil types in Washington County, Tennessee
The most widespread soils are Dewey, Collegedale and Montevallo; the most common drainage class is well drained (76% of the land), and typical topsoil pH is 5.5.
- Well or moderately well drained
- 89% of land · state 85%
- Typical topsoil pH
- 5.5 strongly acidic · state 5.3
- Septic fields very limited
- 64% of land · state 82%
- Subject to flooding
- 12% of land, any frequency · state 15%
Most common soils in Washington County
Share of mapped land
A county is a patchwork of many soils. These 8 cover 63% of the mapped land; 61 named soil series are mapped here in all.
| Soil | Share of land | Drainage | Topsoil pH |
|---|---|---|---|
| Dewey | 27.7% | Well drained | 5.3 |
| Collegedale | 9.0% | Well drained | 5.0 |
| Montevallo | 7.0% | Well drained | 5.3 |
| Greendale | 4.1% | Well drained | 5.8 |
| Bowmantown | 4.0% | Moderately well drained | 6.5 |
| Urban landLand type, not a soil series | 4.0% | — | — |
| Etowah | 3.8% | Well drained | 5.0 |
| Keener | 3.4% | Well drained | 4.8 |
What this means
What the soils in Washington County mean for gardens, lawns and septic systems
For your garden
Typical topsoil in Washington County is strongly acidic: pH 5.5 (most land between 4.8 and 6.5). 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 90% of the land: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silty clay loam (34% 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 64% of the land in Washington County very limited, 26% somewhat limited and 0% not limited (10% not rated, such as urban land, pits or water).
Statewide, 82% of the land is very limited, so Washington 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 12% of the land (5% occasional, <1% 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 (76%). 89% of the land is moderately well drained or better, compared with 85% across Tennessee.
Show as a table
| Category | Washington County | Tennessee |
|---|---|---|
| Excessively drained | 2.7% | 2.0% |
| Somewhat excessively drained | 2.7% | 11.6% |
| Well drained | 75.5% | 57.1% |
| Moderately well drained | 8.2% | 14.7% |
| Somewhat poorly drained | 0.2% | 4.5% |
| Poorly drained | 0.8% | 4.2% |
| Very poorly drained | 0.0% | 0.1% |
| Not rated | 9.9% | 5.9% |
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 | Washington County | Tennessee |
|---|---|---|
| Not limited | 0.0% | 0.1% |
| Somewhat limited | 26.4% | 12.7% |
| Very limited | 63.7% | 81.9% |
| Not rated | 9.9% | 5.3% |
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 | Washington County | Tennessee |
|---|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 2.8% | 9.9% |
| B: moderate infiltration | 51.0% | 39.3% |
| C: slow infiltration | 21.0% | 19.3% |
| D: very slow infiltration (clayey, shallow or wet) | 12.7% | 13.2% |
| A/D: D as is, A if drained | 0.0% | 0.0% |
| B/D: D as is, B if drained | 0.7% | 5.7% |
| C/D: D as is, C if drained | 0.0% | 6.4% |
| Not rated | 11.8% | 6.2% |
Flooding
Show as a table
| Category | Washington County | Tennessee |
|---|---|---|
| No flooding | 79.2% | 80.3% |
| Rare or very rare | 5.4% | 1.4% |
| Occasional | 5.3% | 8.5% |
| Frequent or very frequent | 0.8% | 5.0% |
| Not reported | 9.2% | 4.8% |
Seasonal high water table
Show as a table
| Category | Washington County | Tennessee |
|---|---|---|
| Within 18 inches at some time of year | 1.0% | 12.1% |
| 18 inches to 3.3 feet | 9.0% | 10.5% |
| Deeper than 3.3 feet or none reported | 80.9% | 73.0% |
| Not reported | 9.2% | 4.4% |
Topsoil pH and texture
First mineral layer of each soil
Typical topsoil pH is 5.5 (strongly acidic); 80% of rated land falls between 4.8 and 6.5. Median topsoil organic matter is 1.5%.
Show as a table
| Category | Washington County | Tennessee |
|---|---|---|
| Strongly acidic (below 5.5) | 38.6% | 58.1% |
| Moderately to slightly acidic (5.5–6.4) | 42.4% | 26.3% |
| Near neutral (6.5–7.3) | 8.2% | 9.3% |
| Alkaline (7.4 and up) | 0.8% | 0.1% |
| Not reported | 10.0% | 6.2% |
Texture
Show as a table
| Category | Washington County | Tennessee |
|---|---|---|
| Sandy | 0.3% | 0.7% |
| Loamy (loam, silt loam and similar) | 89.6% | 91.8% |
| Clayey (40%+ clay) | 0.1% | 1.3% |
| Organic (muck or peat) | 0.0% | 0.0% |
| Not reported (rock, urban land, etc.) | 10.0% | 6.2% |
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 County, Tennessee (FIPS 47179): 209,006 acres of mapped land, 2,094 acres of open water excluded. State comparisons pool all mapped land in Tennessee.
- 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.