Whether or not to prune depends on how large the spirea will get and how much room you have for it to grow. Other than cleaning up the ends, a small one will not need pruning. An overgrown spirea can be pruned back in stages. When you prune, cut just above the first set of buds.
HOW DO I PRUNE SPIREA?
When you start seeing leaves and the forecast looks like spring has really arrived in your area, it’s time to prune.