Pruning Summer Flowering Plants
Most hydrangeas, roses, grasses, butterfly bushes and other summer blooming plants can be pruned any time after they become dormant. This requires a (hard) freeze with temps in the lower 20’s. There is no rush to do this.
Some folks like to see the dormant flower heads throughout the winter. The real deadline for pruning these plants is before the spring growth begins. I often prune my plants on a warm day after January 1.
It is detrimental to prune spring-flowering plants (spirea, lilac, azaleas, forsythia) at this time because you will be removing the spring flower buds.
