When to prune shrubs. ✂️ . One of the many “rules of thumb” for when to prune is that you should prune your flowering shrubs just after they finish blooming; this is true for most plants, but there are some caveats. Pruning your trees and shrubs well is fundamental for the health, wellness, and lifespan of your landscape ornamentals. . Different shrubs bloom at different times. Knowing your landscape is important so you don’t accidentally prune early before it’s had a chance to set bud. For fall