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

Rhododendron
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.

Bugleweed
Shares part shade and moderate to high water; blooms in mid spring, before this one opens; low at 6 in, to carpet the ground beneath; evergreen, so the bed keeps its shape through winter.

Pansy
Takes part sun to part shade and moderate to high water; blooms in early spring, before this one opens; low at 8 in, to carpet the ground beneath; both offer pollinator forage, in different months.

Hellebore
Shares part shade and moderate to high water; blooms in late winter, before this one opens; both offer pollinator forage, in different months; evergreen, so the bed keeps its shape through winter.

Globeflower
Takes part sun to part shade and high water; blooms in late spring, before this one opens; both offer pollinator forage, in different months; lower at 2 ft, for the front of the border.

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; taller at 23 ft, for the layer behind it.

Windflower
Takes part sun to part shade and moderate to high water; blooms in early spring, before this one opens; low at 6 in, to carpet the ground beneath; both are strong pollinator plants, and they feed in different months.
Blooming alongside

Lobelia
Takes part sun to part shade and moderate to high water; low at 8 in, to carpet the ground beneath; overlaps, then carries the display into early fall; both are strong pollinator plants.