The living collections are the primary focus of the Arboretum, including hardy woody plants, herbaceous plants, non-hardy (conservatory) plants, and natural habitat communities. All collections in the Arboretum are displayed within an aesthetically pleasing informal garden context and/or a natural-appearing, ecologically sound habitat.

New plants are added to the living collection annually. These plants come from a variety of sources: trades with fellow arboreta, botanical institutions, and plant collectors, seed collected and grown by Arboretum staff, and various nurseries.

Plants in the landscape were initially documented with carefully plotted hand-drawn maps and a card file system. With the hiring of a full-time staff member, the collection records went digital, moving thousands of records into a spreadsheet and mapping every planted tree or shrub with GIS coordinates. Most plants are labeled in the field with a metal identification tag that notes the botanical name, lot number (precursor to discrete accession numbers), and abbreviated source information. Tags have been known to disappear, whether via wind, a lost branch, or occasionally nibbled by a deer with a taste for shiny things, so GIS coordinates are truly essential to keeping track of all 2500 woody plants in the scientific collection at Starhill Forest.