Soils
The soil series groupings that make up the Arboretum area are representative of the soil series commonly found throughout Acton, as mapped by the USDA Natural Resources Conservation Service (NRCS). Soils of similar characteristics are grouped into series named for the place where they were first identified, i.e. Swansea Muck.

In their soil report, the USDA NRCS provides the soil properties for any given series and the soil interpretations: such as Land Capability Classifications, Prime and Locally important Farmland, Woodland Management and Productivity ratings. The predominant soil is mapped; however, most of these mapping units include scattered areas of other soils which may have very different characteristics. The scale of the NRCS mapping does not permit these scattered inclusions to be shown. What is given here for the Arboretum is the broad general soil classification. Therefore, the recording of actual information from on-site experience is important, particularly as it differs from the broad soil series description in the report.

The variety of soils present in the Arboretum affords an opportunity to develop educational materials about plants and soils. Because the soils encompass almost the full range of soil types present within the town, homeowners can learn from Arboretum management and planting techniques. Any time an area of the Arboretum is managed or planted contrary to general recommendations based on its soil characteristics, a careful explanation needs to be provided.

Upper Formal Area
The soil series present in the upper formal area of the Arboretum (from Taylor Road over to the farm ponds and drainage ditch, including the proposed Nursery and parking lot area) are Woodbridge and Charlton, with Woodbridge covering the major portion of the area.

  • WOODBRIDGE series consist of nearly level to steep, deep (5+ feet), moderately well drained soils on drumlins. They formed in compact glacial till. Woodbridge soils have friable fine sandy loam or sandy loam surface soil and subsoil with moderate permeability over a firm, fine sandy loam or sandy loam substratum at 15 to 38 inches, which has slow or very slow permeability. Woodbridge soils have a very stony or extremely stony surface except where stones have been removed, and have stones below the surface. They have a perched, seasonal high water table at 18 to 24 inches. Major limitations are related to wetness, slow permeability in the substratum, stoniness and slope.
  • CHARLTON series consist of gently sloping to steep, deep ( 5+ feet), well drained soils on uplands where the relief is affected by the underlying bedrock. They formed in glacial till ground moraine. Charlton soils are 60 inches or more of friable fine sandy loam surface soil, subsoil and substratum with moderate or moderately rapid permeability. Charlton soils have a very stony or extremely stony surface, except where stones have been removed, and have stones below the surface. Major limitations are related to slope and stoniness.

Woodbridge has a land capability classification of 6s22, and is considered State Important Farmland. It is generally considered unsuitable for cultivation because of severe limitations; being shallow, stony, and droughty. The State Important rating means; however, that given proper cultural practices, the soil is capable of being economically productive farmland. This is the predominant soil in the area of the formal, managed portion of the Arboretum.

Wetlands and Farm Ponds
Whitman is the predominant series running from the farm ponds down to the esker. It is considered a hydric soil (one that is saturated, flooded or ponded long enough during the growing season to develop anaerobic conditions in the upper stratum.) Much of this area at the Arboretum is covered with red maples.

  • WHITMAN series consist of nearly level, deep (5+ ft.), very poorly drained soils in depressions and drainageways of uplands. They formed in compact glacial till. Whitman soils have friable loam or fine sandy loam surface soil and subsoil with moderate or moderately rapid permeability over a firm sandy loam, fine sandy loam or loam substratum (hardpan) at 10 to 30 inches which has slow or very slow permeability. They have a perched high water table at or near the surface most of the year. Whitman soils have a very stony or extremely stoney surface, except where stones have been removed, and have stones below the surface. Major limitations are relative to wetness, slow permeability and stoniness.

Whitman has a land capability classification of 7s23, and has very severe limitations for cultivation. This area is predominately a wetlands area not subject to intense use or development other than minimal activities, such as crossings and the limited introduction of plant material for species and wildlife enhancement.

Esker and Hardwood Forest
The esker and the woodland area running above the bog, along the telephone easement is Hinckley.

  • HINCKLEY series consist of nearly level to very steep, deep (5+ ft.), excessively drained soils on glacial outwash plain, terraces, kames and eskers. They formed in gravelly and cobbly coarse textured glacial outwash. Hinckley soils have friable or loose, gravelly and very gravelly sandy loam to loamy coarse sand surface soil and subsoil with rapid permeability, with loose stratified sands and gravels in the substratum at 12 to 30 inches which have very rapid permeability. Major limitations are related to slope and droughtiness.

Hinckley has a land capability classification of 6s9, and has severe limitations that make them generally unsuitable for cultivation. The limitations are mainly due to it being shallow, stony and droughty.

Bog
The bog itself on the USDA NRCS soil map is shown as Swansea Muck. Actual experience indicates that the bog is indeed a peat bog not a muck area as mapped by the USDA. The peat bog is approximately 16 feet deep from an actual sample boring. Peat bog soils are largely unconsolidated material, largely un-decomposed organic matter that has accumulated under excess moisture, while muck is well-decomposed organic soil material. The area on the Donald's property to the west of the esker is a muck soil.

At the easterly edge of the bog, a small area of Whitman runs parallel to Minot Avenue.

Remainder of the Area
The remainder of the Arboretum is Charlton-Hollis Rock Outcrop Complex, covering the area from the bog and the telephone easement, behind Wood Lane all the way to Main Street. This includes the old pastures and orchards that are in various states of succession.

  • CHARLTON-HOLLIS-ROCK OUTCROP COMPLEX series consist of well drained Charlton soils, somewhat excessively drained Hollis soils and rock outcrops, that occur in such intricate patterns on the landscape, that it is not practical to separate them at the scale of mapping. Generally these areas consist of about 50 percent Charlton soils, 15 percent Hollis soils, 10 percent rock outcrop and 25 percent other soils. Major limitations are related to rockiness and slope, and depth to bedrock in the Hollis soil. For information on Charlton and Hollis soils, see individual series descriptions.
  • HOLLIS series consists of gently sloping to very steep, shallow, somewhat excessively drained soils on bedrock controlled uplands. They formed in a thin mantle of glacial till or residuum from local bedrock. Hollis soils have friable fine sandy loam surface soil and subsoil with moderate or moderately rapid permeability. Depth to bedrock is 10 to 20 inches. Rock outcrops are common, and many areas have stones and boulder on the surface. Major limitations are related to depth to bedrock, rockiness and slope.

The Charlton-Hollis Rock Outcrop Complex has no land capability rating as such, only Charlton has a capability rating. Hollis is not rated for cultivation.