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 kinds (species, varieties or cultivars) of trees or woody plants that have been planted and are growing in accordance with the arboretum plan. Plants in the arboretum collection must be labeled in some way as to identify them taxonomically, including scientific name and cultivar if possible, and documented in some way so that information on their acquisition (source or origin, date of acquisition, etc.) is available for access.
- 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 in fulfillment of the arboretum plan.
- 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.