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

Southern Wax Myrtle
Shares full sun and moderate water; blooms in late winter, before this one opens; both offer pollinator forage, in different months; taller at 17 ft, for the layer behind it; they only overlap in zones 10 to 11.

Indian Hawthorn
Shares full sun and moderate water; blooms in mid spring, before this one opens; both offer pollinator forage, in different months; evergreen, so the bed keeps its shape through winter; they only overlap in zone 10.
Blooming alongside

Pansy
Takes full sun to part sun and moderate water; opens in early spring and overlaps into this one's season; low at 8 in, to carpet the ground beneath.

Nemesia
Shares full sun and moderate water; opens in mid spring and overlaps into this one's season; both offer pollinator forage; low at 12 in, to carpet the ground beneath.

Sunflower
Shares full sun and moderate water; its seed heads stand through winter, for structure and the birds; both offer pollinator forage.

Austin Pretty Limits Oleander
Shares full sun and moderate water; evergreen, so the bed keeps its shape through winter; both offer pollinator forage; echoes the pink; they only overlap in zones 10 to 11.

Blackfoot Daisy
Shares full sun and low to moderate water; overlaps, then carries the display into late fall; evergreen, so the bed keeps its shape through winter; both offer pollinator forage; they only overlap in zones 10 to 11.

Goodding's Verbena
Shares full sun and moderate water; opens in mid spring and overlaps into this one's season; both offer pollinator forage; low at 12 in, to carpet the ground beneath; they only overlap in zones 10 to 11.