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

Snowdrop
Shares part shade and moderate water; blooms in late winter, before this one opens; both offer pollinator forage, in different months; lower at 5 in, for the front of the border.

Camellia
Shares part shade and moderate water; blooms in midwinter, before this one opens; both offer pollinator forage, in different months; evergreen, so the bed keeps its shape through winter; they only overlap in zones 7 to 8.
Taking over as Foam Flower finishes

Northern Sea Oats
Shares part shade and moderate water; blooms in midsummer as this one finishes; its seed heads stand through winter, for structure and the birds; taller at 3.5 ft, for the layer behind it.

Cardinal Flower
Takes part sun to part shade and moderate to high water; blooms in midsummer as this one finishes; both offer pollinator forage, in different months; taller at 3.5 ft, for the layer behind it.

Summersweet
Shares part shade and moderate to high water; blooms in midsummer as this one finishes; both offer pollinator forage, in different months; taller at 6 ft, for the layer behind it.

Ligularia
Shares part shade and moderate to high water; blooms in midsummer as this one finishes; both offer pollinator forage, in different months; taller at 4 ft, for the layer behind it.
Blooming alongside

Hellebore
Shares part shade and moderate water; opens in late winter and overlaps into this one's season; evergreen, so the bed keeps its shape through winter; a soft color beside the white.

Rhododendron
Shares part shade and moderate water; evergreen, so the bed keeps its shape through winter; both offer pollinator forage; taller at 6 ft, for the layer behind it.