Knowing what and what not to prune in May mostly comes down to when a plant flowers. It sounds simple, and it often is. When it comes to shrubs, trees, and climbers, if they flower in spring and have finished, prune them. If they are still flowering or yet to reach their potential, keep those pruning tools away.
That is a very general overview of plants to prune in May, but it applies to many plants. In addition to pruning spring-flowering plants that have finished blooming, you can also cut back perennials before they bloom for a better display come summer. Plus, May is also an opportune time to trim evergreens.
