County soil summary
Soil types in McLennan County, Texas
The most widespread soils are Heiden, Houston Black and Wilson; the most common drainage class is well drained (58% of the land), and typical topsoil pH is 7.9.
- Well or moderately well drained
- 95% of land · state 88%
- Typical topsoil pH
- 7.9 moderately alkaline · state 7.5
- Septic fields very limited
- 82% of land · state 71%
- Subject to flooding
- 13% of land, any frequency · state 10%
Most common soils in McLennan County
Share of mapped land
A county is a patchwork of many soils. These 8 cover 41% of the mapped land; 72 named soil series are mapped here in all.
| Soil | Share of land | Drainage | Topsoil pH |
|---|---|---|---|
| Heiden | 9.2% | Well drained | 8.2 |
| Houston Black | 6.0% | Moderately well drained | 7.9 |
| Wilson | 5.5% | Moderately well drained | 6.5 |
| Aledo | 5.1% | Well drained | 7.8 |
| Slidell | 4.0% | Moderately well drained | 8.0 |
| Lott | 3.7% | Well drained | 8.2 |
| UnnamedGeneral soil group, not a named series | 3.7% | — | — |
| Tinn | 3.6% | Moderately well drained | 7.9 |
What this means
What the soils in McLennan County mean for gardens, lawns and septic systems
For your garden
Typical topsoil in McLennan County is moderately alkaline: pH 7.9 (most land between 6.5 and 8.2). Acid-loving plants such as blueberries and azaleas struggle without amended beds, and some trees and shrubs show iron chlorosis (yellow leaves with green veins).
Clayey topsoil covers 52% 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 clay (29% of the land).
95% of the land is moderately well to excessively drained, which suits most garden plants.
For your lawn and yard
On 86% 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.
For a septic system
For conventional septic absorption fields, NRCS rates 82% of the land in McLennan County very limited, 4% somewhat limited and 0% not limited (14% not rated, such as urban land, pits or water).
Statewide, 71% of the land is very limited, so McLennan County is more 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 13% of the land (3% occasional, 6% 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 (58%). 95% of the land is moderately well drained or better, compared with 88% across Texas.
Show as a table
| Category | McLennan County | Texas |
|---|---|---|
| Excessively drained | 0.0% | 1.0% |
| Somewhat excessively drained | 0.6% | 1.4% |
| Well drained | 57.7% | 69.9% |
| Moderately well drained | 36.3% | 15.8% |
| Somewhat poorly drained | 0.2% | 3.7% |
| Poorly drained | 0.0% | 2.2% |
| Very poorly drained | 0.0% | 0.5% |
| Not rated | 5.2% | 5.6% |
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 | McLennan County | Texas |
|---|---|---|
| Not limited | 0.0% | 1.4% |
| Somewhat limited | 3.9% | 16.7% |
| Very limited | 82.4% | 70.9% |
| Not rated | 13.7% | 11.0% |
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 | McLennan County | Texas |
|---|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 1.7% | 7.2% |
| B: moderate infiltration | 5.6% | 20.0% |
| C: slow infiltration | 24.7% | 22.9% |
| D: very slow infiltration (clayey, shallow or wet) | 61.2% | 38.3% |
| A/D: D as is, A if drained | 0.0% | 0.1% |
| B/D: D as is, B if drained | 0.0% | 0.8% |
| C/D: D as is, C if drained | 0.0% | 1.8% |
| Not rated | 6.7% | 8.8% |
Flooding
Show as a table
| Category | McLennan County | Texas |
|---|---|---|
| No flooding | 83.7% | 86.1% |
| Rare or very rare | 3.6% | 2.1% |
| Occasional | 2.9% | 3.4% |
| Frequent or very frequent | 6.1% | 4.6% |
| Not reported | 3.7% | 3.7% |
Seasonal high water table
Show as a table
| Category | McLennan County | Texas |
|---|---|---|
| Within 18 inches at some time of year | 0.0% | 5.7% |
| 18 inches to 3.3 feet | 0.2% | 3.6% |
| Deeper than 3.3 feet or none reported | 99.8% | 89.0% |
| Not reported | 0.0% | 1.6% |
Topsoil pH and texture
First mineral layer of each soil
Typical topsoil pH is 7.9 (moderately alkaline); 80% of rated land falls between 6.5 and 8.2. Median topsoil organic matter is 2.5%.
Show as a table
| Category | McLennan County | Texas |
|---|---|---|
| Strongly acidic (below 5.5) | 0.0% | 5.2% |
| Moderately to slightly acidic (5.5–6.4) | 5.2% | 9.8% |
| Near neutral (6.5–7.3) | 15.0% | 24.9% |
| Alkaline (7.4 and up) | 64.7% | 46.8% |
| Not reported | 15.1% | 13.3% |
Texture
Show as a table
| Category | McLennan County | Texas |
|---|---|---|
| Sandy | 4.6% | 14.6% |
| Loamy (loam, silt loam and similar) | 27.1% | 56.0% |
| Clayey (40%+ clay) | 52.4% | 15.9% |
| Organic (muck or peat) | 0.0% | 0.1% |
| Not reported (rock, urban land, etc.) | 15.8% | 13.4% |
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
- McLennan County, Texas (FIPS 48309): 663,666 acres of mapped land, 15,496 acres of open water excluded. State comparisons pool all mapped land in Texas.
- 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.