NCPC approves Smithsonian South Mall Campus Phase 2 final plans, endorses curated cultural‑landscape approach

The National Capital Planning Commission approved the Smithsonian Institution’s final Phase 2 plans for the South Mall Campus historic core (including the Smithsonian Castle and surrounding museum gardens) at its May 2 meeting.

Smithsonian Gardens and project staff explained that the Castle’s grounds are a curated cultural landscape maintained as a living museum collection. The Phase 2 work follows Phase 1 conservation and seismic stabilization and focuses on envelope restoration, final perimeter security that is compatible with the Castle’s character, and carefully selected tree and understory planting to restore the gardens after construction. Smithsonian Gardens described a mostly native understory and a tree palette that balances native species with selected noninvasive cultivars that support interpretive and horticultural goals; the team committed to a minimum percentage of native plantings in ongoing garden management.

Public comment and pollinator requests

One public commenter urged adding common and poke milkweed species to better support monarch butterflies and noted concerns about cultivars and non‑native species. Smithsonian Gardens responded that pollinator goals are integral to the design and that plant lists have been curated to match the Castle’s cultural‑landscape character; the team committed to achieve a high native‑plant percentage in the understory and to include pollinator‑friendly species where appropriate.

Decision and implementation

NCPC staff recommended approval and noted that the Castle gardens are a living museum collection that must be curated for interpretive, research and conservation goals. The commission voted to approve the final site and building plans; Smithsonian Gardens will implement the planting plan and maintain living collections consistent with museum stewardship policies.