1. Prune in Winter - Crape myrtles should be pruned in the winter-time, when they are dormant and don't have any leaves. How much you prune is up to you. There is no need to do a severe prune (sometimes called 'crape murder'), but trimming back overall height if needed and thinning the branches will help the tree flush out well in spring. If you missed pruning in the winter, you can always prune later, just wait until after bloom time, otherwise you will cut off all of those beautiful flowers.