Companion plants for Ninebark
Ninebark blooms from May through June. It wants full sun and moderate water. The 8 companion pairings below each state why the pairing works.
Taking over as Ninebark finishes

Carnival Scotch Heather
Shares full sun and moderate water; overlaps, then carries the display into late summer; low at 8 in, to carpet the ground beneath; both are strong pollinator plants.

Brown-Eyed Susan
Shares full sun and moderate water; blooms in midsummer 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.

Sneezeweed
Shares full sun and moderate water; blooms in midsummer 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.

Prairie Blazing Star
Shares full sun and moderate water; blooms in midsummer 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.

Buffalograss
Shares full sun and low to moderate water; overlaps, then carries the display into late summer; low at 8 in, to carpet the ground beneath; both are strong pollinator plants.

Purple Lovegrass
Shares full sun and low to moderate water; blooms in midsummer 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.
Blooming alongside

Windflower
Takes full sun to part sun and moderate 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.

Kinnikinnick
Shares full sun and moderate water; opens in mid spring and overlaps into this one's season; low at 8 in, to carpet the ground beneath; both are strong pollinator plants.