Companion plants for Obedient Plant
Obedient Plant blooms from August through September. It wants full sun and moderate water. The 8 companion pairings below each state why the pairing works.
Blooming before Obedient Plant opens

Snow-in-Summer
Shares full sun and low to moderate water; blooms in late spring, before this one opens; low at 6 in, to carpet the ground beneath; evergreen, so the bed keeps its shape through winter.

Japanese Stewartia
Takes full sun to part sun and moderate water; blooms in early summer, before this one opens; taller at 16 ft, for the layer behind it; its white flowers settle the pink.

Gardenia
Takes full sun to part sun and moderate to high water; blooms in late spring, before this one opens; evergreen, so the bed keeps its shape through winter; its white flowers settle the pink; they only overlap in zones 8 to 9.

Queen of the Prairie
Shares full sun and moderate to high water; blooms in early summer, before this one opens; both are North American natives; echoes the pink.

Blue Oat Grass
Shares full sun and low to moderate water; blooms in early summer, before this one opens; evergreen, so the bed keeps its shape through winter; lower at 2.5 ft, for the front of the border; this one spreads, so it will crowd its neighbor in time.
Blooming alongside

Arborvitae
Shares full sun and moderate water; evergreen, so the bed keeps its shape through winter; taller at 20 ft, for the layer behind it; both are North American natives.

Colorado Blue Spruce
Shares full sun and moderate water; evergreen, so the bed keeps its shape through winter; both are North American natives.

Bee Balm
Shares full sun and moderate water; opens in midsummer and overlaps into this one's season; both are North American natives; red sits close to pink on the wheel.