When can a garden hedge be cut?

A common answer is "when the saw is sharp", meaning that if you need to cut it, cut it when you are ready to do the work. Having said that, in general it is best to cut flowering plants just after they finish blooming (to avoid cutting off next year's blooms, which often are set shortly after this year's bloom ends) or in the late winter, before the hedge begins to show new growth. So, it depends on whether you need to consider blooming. Repost question with the name of the hedge plant and we will provide a more specific answer.