Space plants according to ultimate growth of the species you’ve chosen. Choose a sunny location, with good, well-drained soil.
Spiraea is relatively carefree. Prune summer-blooming types in early spring as needed for shaping. Prune spring-blooming types immediately after flowers fade by removing a few of the oldest stems to ground level. If desired, flower clusters can be removed after blooming.
Zones (various) 4-9