Welkinweir is a 197-acre (80 ha) nonprofit arboretum, garden, mansion, and conservation area located at 1368 Prizer Road, East Nantmeal Township, Pennsylvania, United States near Pottstown. It is part of the Hopewell Big Woods. It is open to the public daily without charge.
Welkinweir was the home of Everett and Grace Rodebaugh, founding members of the conservation-minded Green Valleys Association, who bought the site in the 1930s and spent decades improving it. Their house was built in 1940, building upon a much smaller house, built in two sections c. 1750 and c. 1830. Architect Fridtjof Tobiessen designed the 1940 mansion. The property was placed into a conservation easement in 1976, donated to the association in 1997, and is now its headquarters and educational center. In 2001 the estate was listed on the National Register of Historic Places.
Its arboretum includes cherry, dogwood, dwarf evergreens, franklinia, magnolia, Japanese maple, swamp and sugar maple, and sweetgum, as well as azaleas and rhododendrons.