When do I prune flowering shrubs? It’s so confusing.
Each May and June I’m asked, “Why didn’t my lilacs bloom?” only to find out in the next sentence that the questioners had literally nipped the plants in the (flower)bud with late summer, fall, winter or earliest springtime pruning, long after the new year’s blossoms had been set.
Early bloomers flower on old wood. Go out and look at a forsythia or a lilac in winter or early spring: Unless you pruned in summer or fall, you’ll see flower buds already in place, dormant but there. If you prune them off, it won’t flower that year. Make sense? It will not harm the plant to prune extra-early, but why not enjoy the blooms first?
Generally speaking, if you want flowers next year, don’t prune spring-blooming shrubs and trees more than a month or so after they finish blooming, meaning not from late spring or earliest summer, or again until after the next spring’s bloom cycle. After they’re finished flowering, prune immediately.
Woody plants that flower late in the season, such as Hydrangea paniculata, bloom on new wood. Again, go out and look. You don’t see any flower buds in early spring, do you? Discovering where on the stems and when the plant creates its flower buds will help direct your pruning efforts.
Major rejuvenation pruning, when required, I do in spring, to allow the plant the entire season to recover. Sometimes I wait selfishly until after bloom; sometimes I sacrifice bloom in the name of getting the job done asap. One time I never prune (except the 3-D’s, above) in my cold-winter zone: in fall. I don’t want new growth to sprout and then get hit by blasts of cold. Avoid undertaking rejuvenations late in the season.