when to trim spirea
Thank you for the question. Since you indicate that your spirea bloom in summer, they are likely a cultivar of Spiraea x bumalda or Spiraea japonica. They bloom on "new wood" or new growth that emerges in spring from the base of the plant. In this case, you should prune these types of spirea in late fall or winter. It's OK to remove a few stragglers now but you should leave most of the foliage to allow the shrub to store up energy for the rest of the summer.
Thank you for contacting Extension.