The Arboretum at South Seattle College is a 5.5-acre botanical garden, featuring several unique gardens, including a rose garden and a world-class conifer collection. It is both a classroom for students and a public garden enjoyed by the community at large.
But in 1978, when horticulture students petitioned to create this outdoor classroom, the available land at the north end of the campus was hardly promising. South Seattle College was built on the site where the City of Seattle Department of Engineering had its sand and gravel operations for many years, so there was very little of what could be called "soil." To make matters worse, in the early days of classes, students learning to use heavy equipment used the site to practice, and that compacted the surface even more. It was better suited to being a parking lot than a garden.
At the time, Seattle Metro (not to be confused with King County Metro) was promoting the use of biosolids – treated sewage sludge – for making compost and improving soils in parks and on forest land. SSC and Seattle Metro teamed up to grade the area where the Arboretum was to be situated, cover it with 18" of sludge, and plant ryegrass, which was later tilled in. Despite this effort and the addition of topsoil for new gardens, drainage remains poor in the Arboretum.
In 2014, the Arboretum was designated an American Conifer Society Reference Garden because it contains one of the best collections of conifers in the United States.
The Arboretum became a National Wildlife Federation Urban Wildlife Sanctuary in 2012.
The Coenosium Rock Garden was inducted into the Gardens for Peace program in 2010.
The Landscape Horticulture facilities and the Arboretum were awarded a 5-star EnviroStars rating in 2010.
The Arboretum has been pesticide-free since 2008.