Prune spirea immediately after the spring bloom season, according to SFGate. Pruning can make some spirea varieties have a second bloom season. Spirea grows in USDA Hardiness Zones of 5 to 9.
To prune a maintained spirea, take clean, sharp pruning shears and clip just to the topmost leaf bud on each of the branches. Always remove dead or diseased limbs whenever possible, without worry to the season. Also, remove completely any crossed branches to keep a uniform shape. In the fall, overgrown spirea plants can be cut down to 8 to 12 inches from the ground to encourage growth in the spring.