When do you prune perennials? Well, some perennials are evergreen and can be left standing as is during the winter for visual interest. Other perennials are left standing for a different reason, notes Marie Iannotti: they "simply don’t fare well if they are pruned too late in the season." Either way, now that spring is here, it's time to prune such perennials. About's Gardening Guide identifies them is this article on when to prune perennials.