County soil summary
Soil types in St. Charles County, Missouri
The most widespread soils are Menfro, Harvester and Goss; the most common drainage class is well drained (27% of the land), and typical topsoil pH is 6.6.
- Well or moderately well drained
- 56% of land · state 67%
- Typical topsoil pH
- 6.6 neutral · state 6.0
- Septic fields very limited
- 90% of land · state 93%
- Subject to flooding
- 43% of land, any frequency · state 20%
Most common soils in St. Charles County
Share of mapped land
A county is a patchwork of many soils. These 8 cover 45% of the mapped land; 60 named soil series are mapped here in all.
| Soil | Share of land | Drainage | Topsoil pH |
|---|---|---|---|
| Menfro | 7.5% | Well drained | 5.5 |
| Harvester | 7.1% | Moderately well drained | 5.1 |
| Goss | 6.1% | Well drained | 6.0 |
| Urban landLand type, not a soil series | 6.1% | — | — |
| Carlow | 5.6% | Poorly drained | 6.8 |
| Portage | 4.4% | Very poorly drained | 6.2 |
| Armster | 4.4% | Moderately well drained | 6.0 |
| Dockery | 3.8% | Somewhat poorly drained | 6.8 |
What this means
What the soils in St. Charles County mean for gardens, lawns and septic systems
For your garden
Typical topsoil in St. Charles County is neutral: pH 6.6 (most land between 5.6 and 7.7), the range most vegetables, flowers and lawn grasses prefer.
Loamy topsoil (loam, silt loam and similar) covers 83% of the land: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (60% of the land).
For your lawn and yard
On 79% of the land, rain soaks in slowly (hydrologic groups C and D, including dual groups that are D until drained). Expect runoff and puddles after heavy rain: core-aerate compacted lawns and keep ground sloping away from foundations.
A seasonal high water table comes within 18 inches of the surface on 28% of the land, often in spring. Basements, sump pumps and lawns in low spots feel it first.
For a septic system
For conventional septic absorption fields, NRCS rates 90% of the land in St. Charles County very limited, 4% somewhat limited and 0% not limited (6% not rated, such as urban land, pits or water).
That is close to the state as a whole (93% very limited).
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 43% of the land (28% occasional, 11% 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 (27%). 56% of the land is moderately well drained or better, compared with 67% across Missouri.
Show as a table
| Category | St. Charles County | Missouri |
|---|---|---|
| Excessively drained | 0.7% | 1.0% |
| Somewhat excessively drained | 0.9% | 7.9% |
| Well drained | 27.3% | 29.2% |
| Moderately well drained | 26.7% | 28.8% |
| Somewhat poorly drained | 16.5% | 18.1% |
| Poorly drained | 15.6% | 13.0% |
| Very poorly drained | 5.8% | 0.6% |
| Not rated | 6.4% | 1.5% |
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 | St. Charles County | Missouri |
|---|---|---|
| Not limited | 0.0% | 0.0% |
| Somewhat limited | 3.5% | 6.1% |
| Very limited | 90.2% | 92.9% |
| Not rated | 6.2% | 1.0% |
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 | St. Charles County | Missouri |
|---|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 2.2% | 3.8% |
| B: moderate infiltration | 12.6% | 15.7% |
| C: slow infiltration | 26.3% | 27.6% |
| D: very slow infiltration (clayey, shallow or wet) | 30.8% | 31.2% |
| A/D: D as is, A if drained | 0.0% | 0.0% |
| B/D: D as is, B if drained | 4.0% | 2.9% |
| C/D: D as is, C if drained | 17.6% | 17.2% |
| Not rated | 6.4% | 1.6% |
Flooding
Show as a table
| Category | St. Charles County | Missouri |
|---|---|---|
| No flooding | 56.3% | 80.2% |
| Rare or very rare | 4.5% | 4.1% |
| Occasional | 28.3% | 9.4% |
| Frequent or very frequent | 10.6% | 6.1% |
| Not reported | 0.2% | 0.2% |
Seasonal high water table
Show as a table
| Category | St. Charles County | Missouri |
|---|---|---|
| Within 18 inches at some time of year | 28.1% | 27.8% |
| 18 inches to 3.3 feet | 33.8% | 29.2% |
| Deeper than 3.3 feet or none reported | 38.0% | 42.9% |
| Not reported | 0.0% | 0.1% |
Topsoil pH and texture
First mineral layer of each soil
Typical topsoil pH is 6.6 (neutral); 80% of rated land falls between 5.6 and 7.7. Median topsoil organic matter is 2.4%.
Show as a table
| Category | St. Charles County | Missouri |
|---|---|---|
| Strongly acidic (below 5.5) | 0.4% | 22.1% |
| Moderately to slightly acidic (5.5–6.4) | 40.3% | 45.6% |
| Near neutral (6.5–7.3) | 38.9% | 28.6% |
| Alkaline (7.4 and up) | 14.1% | 2.1% |
| Not reported | 6.4% | 1.6% |
Texture
Show as a table
| Category | St. Charles County | Missouri |
|---|---|---|
| Sandy | 1.3% | 1.0% |
| Loamy (loam, silt loam and similar) | 82.6% | 94.6% |
| Clayey (40%+ clay) | 9.7% | 2.8% |
| Organic (muck or peat) | 0.0% | 0.0% |
| Not reported (rock, urban land, etc.) | 6.4% | 1.6% |
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
- St. Charles County, Missouri (FIPS 29183): 357,331 acres of mapped land, 22,689 acres of open water excluded. State comparisons pool all mapped land in Missouri.
- 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.