Level II-accredited arboreta have met the following enhanced levels of arboretum standards:
- Satisfy all criteria for Level I accreditation.
- Larger arboretum collection with a minimum number of 100 species, varieties or cultivars of trees or woody plants.
- Arboretum collections policy that describes the development and professional management of the plants in the arboretum collection, in accordance with standards developed in the public garden and museum fields with consideration given to the Saint Louis Declaration regarding invasive species. Such a policy and related practices includes a rationale for holding the particular collections of the arboretum, and collections inventory and record-keeping practices.
- One or more arboretum employees who have job responsibilities that specifically include management or operation of the arboretum.
- Enhanced educational and public programming beyond the base level required in Level I accreditation. Programs must be related to trees (e.g. tree identification, ecology, conservation, collections, or some other tree-focused aspect of the arboretum mission or master plan.