Unlike hydrangea, known for its fluffy, large blooms, gardenia has relatively small flowers. This juxtaposition in size and shape looks very polished side by side.
The dark green leaves of gardenias help break up some of the colors when planted next to hydrangeas, which keeps the overall landscape from looking busy.
Despite their differences in the size of their leaves and floral displays, the two share the same soil preferences, needing fertile, well-draining soil that stays moist.