County soil summary
Soil types in Merrimack County, New Hampshire
The most widespread soils are Tunbridge, Lyman and Becket; the most common drainage class is well drained (39% of the land), and typical topsoil pH is 4.8.
- Well or moderately well drained
- 79% of land · state 69%
- Typical topsoil pH
- 4.8 very strongly acidic · state 4.8
- Septic fields very limited
- 95% of land · state 79%
- Subject to flooding
- 3% of land, any frequency · state 2%
Most common soils in Merrimack County
Share of mapped land
A county is a patchwork of many soils. These 8 cover 36% of the mapped land; 75 named soil series are mapped here in all.
| Soil | Share of land | Drainage | Topsoil pH |
|---|---|---|---|
| Tunbridge | 6.8% | Well drained | 4.8 |
| Lyman | 5.8% | Somewhat excessively drained | 4.0 |
| Becket | 5.7% | Well drained | 4.2 |
| Skerry | 3.7% | Moderately well drained | 5.2 |
| Montauk | 3.6% | Well drained | 5.6 |
| Millsite | 3.5% | Well drained | 5.0 |
| Metacomet | 3.5% | Moderately well drained | 4.5 |
| Henniker | 3.3% | Well drained | 4.7 |
What this means
What the soils in Merrimack County mean for gardens, lawns and septic systems
For your garden
Typical topsoil in Merrimack County is very strongly acidic: pH 4.8 (most land between 4.2 and 5.5). 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 67% of the land: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is fine sandy loam (58% of the land).
79% of the land is moderately well to excessively drained, which suits most garden plants.
For your lawn and yard
On 73% 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 25% 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 95% of the land in Merrimack County very limited, 4% somewhat limited and <1% not limited.
Statewide, 79% of the land is very limited, so Merrimack 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.
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 (39%). 79% of the land is moderately well drained or better, compared with 69% across New Hampshire.
Show as a table
| Category | Merrimack County | New Hampshire |
|---|---|---|
| Excessively drained | 5.8% | 5.2% |
| Somewhat excessively drained | 14.4% | 11.2% |
| Well drained | 38.6% | 37.5% |
| Moderately well drained | 19.9% | 15.0% |
| Somewhat poorly drained | 0.2% | 0.3% |
| Poorly drained | 10.1% | 8.7% |
| Very poorly drained | 8.5% | 5.0% |
| Not rated | 2.4% | 17.1% |
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 | Merrimack County | New Hampshire |
|---|---|---|
| Not limited | 0.6% | 0.2% |
| Somewhat limited | 4.0% | 5.3% |
| Very limited | 95.4% | 79.1% |
| Not rated | 0.0% | 15.4% |
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 | Merrimack County | New Hampshire |
|---|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 12.6% | 11.7% |
| B: moderate infiltration | 12.7% | 17.2% |
| C: slow infiltration | 35.0% | 24.2% |
| D: very slow infiltration (clayey, shallow or wet) | 16.5% | 13.2% |
| A/D: D as is, A if drained | 7.7% | 4.3% |
| B/D: D as is, B if drained | 3.2% | 3.9% |
| C/D: D as is, C if drained | 10.2% | 8.5% |
| Not rated | 2.1% | 17.0% |
Flooding
Show as a table
| Category | Merrimack County | New Hampshire |
|---|---|---|
| No flooding | 97.0% | 83.3% |
| Rare or very rare | 0.0% | 0.0% |
| Occasional | 0.7% | 0.5% |
| Frequent or very frequent | 2.2% | 1.7% |
| Not reported | 0.1% | 14.4% |
Seasonal high water table
Show as a table
| Category | Merrimack County | New Hampshire |
|---|---|---|
| Within 18 inches at some time of year | 25.4% | 19.3% |
| 18 inches to 3.3 feet | 22.3% | 15.2% |
| Deeper than 3.3 feet or none reported | 52.3% | 52.2% |
| Not reported | 0.1% | 13.4% |
Topsoil pH and texture
First mineral layer of each soil
Typical topsoil pH is 4.8 (very strongly acidic); 80% of rated land falls between 4.2 and 5.5. Median topsoil organic matter is 4%.
Show as a table
| Category | Merrimack County | New Hampshire |
|---|---|---|
| Strongly acidic (below 5.5) | 79.7% | 70.4% |
| Moderately to slightly acidic (5.5–6.4) | 13.3% | 8.5% |
| Near neutral (6.5–7.3) | 0.1% | 0.2% |
| Alkaline (7.4 and up) | 0.0% | 0.1% |
| Not reported | 7.0% | 20.8% |
Texture
Show as a table
| Category | Merrimack County | New Hampshire |
|---|---|---|
| Sandy | 20.6% | 11.6% |
| Loamy (loam, silt loam and similar) | 66.5% | 64.6% |
| Clayey (40%+ clay) | 0.0% | 0.0% |
| Organic (muck or peat) | 10.3% | 6.5% |
| Not reported (rock, urban land, etc.) | 2.6% | 17.3% |
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
- Merrimack County, New Hampshire (FIPS 33013): 595,709 acres of mapped land, 15,408 acres of open water excluded. State comparisons pool all mapped land in New Hampshire.
- 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.