I hear some version of this question at the register almost every week in late summer: what's actually worth planting right now? Boise sits mostly in USDA Zone 6b, with pockets closer to 7a in town, and that shapes this list more than anything trending online.
Trees and shrubs, get them in the ground now. Fall planting gives roots months to establish in cooling soil before next summer's heat arrives, without the stress of pushing new top growth at the same time. Serviceberry, dwarf Korean lilac, and select Japanese maples are all solid choices for our climate and are typically on our benches through October.
Perennials divide and transplant well in early fall too. If your Russian sage or coneflowers have outgrown their spot, this is the window to split them and either fill in gaps elsewhere in your yard or bring divisions to a neighbor.
Cold-hardy annuals — mums and pansies, mainly — are what keep containers looking alive once summer annuals fade. Pansies in particular will often survive a light frost and keep blooming into November here.
What I'd hold off on: anything borderline-hardy that needs a full season to establish before winter, like some ornamental grasses or broadleaf evergreens. If you're not sure whether something on our bench is fall-safe for your specific yard, ask — that's a five-minute conversation that saves you a spring replant.
Zone guidance is a starting point, not a guarantee — microclimates in your own yard (a south-facing wall, a low frost pocket) matter as much as the zone map. When in doubt, bring us a photo of the spot you're planting and we'll work from there.