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

Rosemary
Shares full sun and low to moderate water; blooms in early spring, before this one opens; both offer pollinator forage, in different months; evergreen, so the bed keeps its shape through winter.

Wisteria
Shares full sun and moderate water; blooms in mid spring, before this one opens; both offer pollinator forage, in different months; purple sits close to blue on the wheel.

Eastern Redbud
Takes full sun to part sun and moderate water; blooms in mid spring, before this one opens; both offer pollinator forage, in different months.
Taking over as Agapanthus finishes

Perennial Sunflower
Shares full sun and moderate water; overlaps, then carries the display into mid fall; its seed heads stand through winter, for structure and the birds; both offer pollinator forage.

Ironweed
Shares full sun and moderate water; overlaps, then carries the display into early fall; its seed heads stand through winter, for structure and the birds; both offer pollinator forage.

Autumn Crocus
Shares full sun and moderate water; blooms in early fall as this one finishes; lower at 6 in, for the front of the border; both offer pollinator forage, in different months.

Switchgrass
Shares full sun and low to moderate water; overlaps, then carries the display into mid fall; its seed heads stand through winter, for structure and the birds; both offer pollinator forage.
Blooming alongside

False Indigo
Shares full sun and low to moderate water; opens in late spring and overlaps into this one's season; its seed heads stand through winter, for structure and the birds; both offer pollinator forage.