Tyler Arboretum’s Pink Hill offers visitors a chance to see the last remaining serpentine barren in Delaware County, and an ecosystem that is found only a few places in the world.
In the Eastern United States, serpentine areas occur in scattered pockets from Alabama to Canada, but the most diverse and botanically significant outcrops are in southeastern Pennsylvania and northern Maryland, including Delaware County.
Over the years, the serpentine barrens of the County have disappeared under suburbia’s sprawl, but many of the plants that grew in these specialized habitats will make the transition to the suburban landscape with surprising ease. By using these plants, home gardeners can help preserve the County’s distinctive landscape.
The serpentine barren (or grassland) is a habitat that has adapted to growing on thin, coarse soil loaded with minerals that are highly toxic to most plants. The toxic soil is a byproduct from the erosion of Serpentine bedrock just below the soils’ surface. Serpentine or Serpentinite – rumored to have been named for a particular snake indigenous to Serpentine areas in the wilds of Italy – is a soft rock with the swirled green and brown color of melted mint chocolate chip ice cream.
The term “barren” often associated with these sites originates from a term the early settlers used to describe the soil’s inability to support commercial crops. The green color comes from the rocks’ high concentration of magnesium. Magnesium itself is very efficient at hampering plants’ nutrient absorbing capabilities; pockets of chromium, cobalt, nickel and iron substantially contribute to the hostile environment.
However, some plants have found a competitive advantage in this harsh soil. While a few species such as the serpentine aster (Aster depauperatus) are found exclusively on Serpentine grasslands, most are fairly common in other parts of the country. Some are native to the prairies of the Midwest, finding a niche in the barrens as fire suppression practices took effect. Others are common to the local area, and several of them are available in the nursery trade.
Pink Hill is named for the pink wash of Phlox subulata or moss phlox that blooms in the spring. Moss phlox is quite easy to find for purchase and is available in a number of colors. Used as a groundcover in hot, dry areas, Phlox subulata literally covers itself with flowers early in the year.
Evergreen except in very exposed areas, moss phlox won’t grow much taller than about three inches, but it can spread laterally for three feet.
To read more in depth about Pink Hill, see the Pink Hill Serpentine Barrens Restoration and Management Plan Report. https://www.tylerarboretum.org/wp-content/uploads/2013/04/Latham-PinkHillReport-2008.pdf