Companion plants for Astilbe
Astilbe blooms from June through July. It wants part shade and high water. The 8 companion pairings below each state why the pairing works.
Blooming before Astilbe opens

Pinxterbloom Azalea
Shares part shade and moderate to high water; blooms in mid spring, before this one opens; both are strong pollinator plants, and they feed in different months; evergreen, so the bed keeps its shape through winter.

Drooping Leucothoe
Shares part shade and moderate to high water; blooms in late spring, before this one opens; both are strong pollinator plants, and they feed in different months; evergreen, so the bed keeps its shape through winter.

Tall Oregon Grape
Shares part shade and moderate to high water; blooms in early spring, before this one opens; both are strong pollinator plants, and they feed in different months; evergreen, so the bed keeps its shape through winter.

Flowering Dogwood
Shares part shade and moderate to high water; blooms in mid spring, before this one opens; both are strong pollinator plants, and they feed in different months; its white flowers settle the pink.
Taking over as Astilbe finishes

Zigzag Goldenrod
Shares part shade and moderate to high water; blooms in late summer as this one finishes; both are strong pollinator plants, and they feed in different months; its seed heads stand through winter, for structure and the birds.

Blue Wood Aster
Shares part shade and moderate to high water; blooms in late summer as this one finishes; both are strong pollinator plants, and they feed in different months; its seed heads stand through winter, for structure and the birds.

Northern Sea Oats
Shares part shade and moderate to high water; overlaps, then carries the display into early fall; both are strong pollinator plants; its seed heads stand through winter, for structure and the birds.
Blooming alongside

Woodland Stonecrop
Shares part shade and moderate to high water; opens in mid spring and overlaps into this one's season; both are strong pollinator plants; evergreen, so the bed keeps its shape through winter.