Soils of Northeastern Pennsylvania

Basic soil: clay, silt and sand

All soils are composed of varying combinations of clay, silt and sand, which is nothing more than weathered rock and always with particles of less than 2 millimeters in diameter. Sandy soils are the most porous and best drained; clay soils hold moisture and slow drainage, and silts provide substantial nutrition to plants.

Sources for soils in the Pocono region are from the weathering of sandstones, shales and limestones or, as a consequence of glaciation, varying combinations of all three. The impact on plant life is enormous because the mineral content of the soils differs; this in turn sets up different combinations of plants that have adapted to conditions that may be very specific or very broad. The result can be success or failure with plant selections for gardens; hence understanding and adapting to local soils may have some value for the landscaper.

Clay as a soil separate consists of mineral soil particles less than 0.002 millimeter in diameter. Clay content is given as a percentage, by weight, of the soil material that is less than 2 millimeters in diameter. How much and what kind of clay impacts the fertility and physical condition of the soil and its ability to react chemically and retain water. Clays influence shrink-swell potential, and thus drainage, as well as saturated hydraulic conductivity, plasticity, the ease of soil dispersion, and other soil properties.

Silt as a soil separate consists of mineral soil particles that are 0.002 to 0.05 millimeter in diameter. Silt content is given as a percentage, by weight, of the soil material that is less than 2 millimeters in diameter.

Silt is easily transported in water or other liquids and is sufficiently fine to be carried great distances by air in the form of dust. Silt is more typically transported by streams or by water currents in the ocean. The intermediate size of the particles strongly impact soil fertility, being the most efficient source of minerals for plants.

Sand as a soil separate consists of mineral soil particles that are 0.05 millimeter to 2 millimeters in diameter. Sand content is listed as a percentage, by weight, of the soil material that is less than 2 millimeters in diameter.

Sandy soils are easily worked, drain well and warm up quickly in spring. Because they keep the soil from compaction, water can easily pass, improving drainage as a counter to the content of clay and organic matter, which impedes flow and holds water, respectivley.

The content of sand, silt, and clay affects the physical behavior of a soil, its relative fertility, and can dramatically effect groundwater and riparian supply.

Soil composition varies widely in northeastern Pennsylvania, but sandy loams are common and thus soils tend to be well drained and on the dry side. Exceptions are bottomlands, swamps and other wetlands where silt and clay content range much higher.

Soils can be altered, but usually at great expense and with substantial difficulty. Home landscaping success is more attainable when plant selections match the soils on site.

Organic matter

Organic matter is the plant and animal residue in the soil at various stages of decomposition. The estimated content of organic matter is expressed as a percentage, by weight, of the soil material that is less than 2 millimeters in diameter.

The content of organic matter in a soil can be maintained by returning crop residue to the soil. Organic matter has a positive effect on available water capacity, water infiltration, soil organism activity, and tilth. It is a source of nitrogen and other nutrients for crops and soil organisms. An irregular distribution of organic carbon with depth may indicate different episodes of soil deposition or soil formation. Soils that are very high in organic matter have poor engineering properties and subside upon drying.

Many forest soils are surprisingly lean in organic matter - just one or two percent being relatively common.

In a normal forest ecosystem, a series of layers of decomposing organic materials - generally leaf litter, twigs and branches, last season's herbaceous plant matter and the remains of a variety of animal life create layers. At the top is fresh material, and at the bottom is a thin veneer of completely decomposed matter that now provides nutrition to plant roots below.

A consequence of disturbing these layers, to which most local species of plants have successfully adapted and upon which they rely, is to strip away the ongoing supply of nutrition, moisture and temperature regulation and the organic balance to which a specific ecosystem has adapted.

Flooding and ponding

Flooding is the temporary inundation of an area caused by overflowing streams, by runoff from adjacent slopes, or by tides. Water standing for short periods after rainfall or snowmelt is not considered flooding, and water standing in swamps and marshes is considered ponding rather than flooding.

Frequency is expressed as none, very rare, rare, occasional, frequent, and very frequent.

"None" means that flooding is not probable. The chance of flooding is nearly 0 percent in any year. Flooding occurs less than once in 500 years.

"Very rare" means that flooding is very unlikely but possible under extremely unusual weather conditions. The chance of flooding is less than 1 percent in any year.

"Rare" means that flooding is unlikely but possible under unusual weather conditions. The chance of flooding is 1 to 5 percent in any year.

"Occasional" means that flooding occurs infrequently under normal weather conditions. The chance of flooding is 5 to 50 percent in any year.

"Frequent" means that flooding is likely to occur often under normal weather conditions. The chance of flooding is more than 50 percent in any year but is less than 50 percent in all months in any year.

"Very frequent" means that flooding is likely to occur very often under normal weather conditions. The chance of flooding is more than 50 percent in all months of any year.

Ponding is standing water in a closed depression. The water is removed only by deep percolation, transpiration, or evaporation or by a combination of these processes. Ponding frequency classes are based on the number of times that ponding occurs over a given period. Frequency is expressed as none, rare, occasional, and frequent.

"None" means that ponding is not probable. The chance of ponding is nearly 0 percent in any year.

"Rare" means that ponding is unlikely but possible under unusual weather conditions. The chance of ponding is nearly 0 percent to 5 percent in any year.

"Occasional" means that ponding occurs, on the average, once or less in 2 years. The chance of ponding is 5 to 50 percent in any year.

"Frequent" means that ponding occurs, on the average, more than once in 2 years. The chance of ponding is more than 50 percent in any year.

Soil acidity (pH)

Soil reaction is a measure of acidity or alkalinity. It is important in selecting crops and other plants, in evaluating soil amendments for fertility and stabilization, and in determining the risk of corrosion. The most common soil laboratory measurement of pH is the 1:1 water method. A crushed soil sample is mixed with an equal amount of water, and a measurement is made of the suspension.

Soils in northeastern Pennsylvania commonly range from about pH 5.5 to 6.2, but can drop very low in bogs and somewhat alkaline in areas with high concentrations of limestone. Neutral - that is, neither acidic or alkaline, is 7.0. To gain a perspective, successful lawns are in a soil with a pH of about 6.8; hence lime is often added to soil surfaces to raise woodland pH to a satisfactory level for grass. In the meantime, a higher soil pH is unhelpful for trees, which have evolved for much more acidic conditions. The consequence of a perfect lawn, then, is to cause harm to the trees we so cherish on wooded homesites.