Prune your spirea in one of two seasons, depending on what type you have. If your spirea plant flowers on old wood stems, cut the plant immediately after it has finished flowering. Otherwise, cut the plant in the early spring before it starts growing.
Choose a first branch to cut, and make the cut at a 90-degree angle to the branch, 4 to 6 inches above the ground.
Continue lopping off the branches until you have cut the entire bush down to the ground. Wipe the blades of your pruning shears with rubbing alcohol between cuts. This cleaning will help prevent infections or diseases from spreading into the plant.
Water the spirea plant normally after pruning. The plant will quickly start growing again thanks to its hardy nature.