Spring Shrub Pruning

White clethra summersweet that can be pruned in spring
Spring in the Northeast can be very demanding. The beautiful snow has probably covered a lot of debris in your flower gardens, from broken branches strewn about to misplaced driveway gravel. In general people know how to tidy up, but we do regularly get phone calls beginning in early April inquiring about shrub pruning. Shrub pruning can be simplified into two seasons; spring pruning and summer pruning.
Pink spirea shrub that can be pruned in spring
Spirea can be pruned in spring
Spring Pruning
Any shrub that blooms in the summer or early autumn can be pruned in the spring. These plants bloom on new wood. The term 'new wood' refers to that season's growth. In terms of actual shrub growing, the season in Vermont begins in late March or early April and ends around late July.
We will use the Hydrangea paniculata treeform for our spring pruning example. This plant puts out masses of large flowers starting in August. Each spring we severely prune the plants growing for sale at the nursery. For the entire spring they look like sticks with stunted branches. However, once the temperatures warm up they will start to put on new growth. In August, those stubby little branches will be three feet long with enormous flower heads that formed and matured during the growing season. The summer-blooming spirea, like 'Little Princess, 'Pink Parasols' and 'Anthony Waterer' are some more shrubs that would benefit from a sharp spring pruning.
Pruned treeform hydrangea paniculata in spring
We severely prune Hydrangea paniculata in spring
Pink flowering hydrangea paniculata treeform in summer
A season of growth makes a difference!
Pruning Tips
How far back you prune a shrub is really a matter of taste. We like a shrub to maintain its natural shape. In order to ensure this we always recommend that people prune the branches at least a foot or more back than the ultimately desired height. This will eliminate what we in the nursery business call 'flat top' or 'bank jobs' (have you ever noticed how the shrubs at a bank always look like boxes?!). We are convinced all those badly pruned shrubs are mortified at their appearance and wish they had a big evergreen they could hide behind. So, if a shrub in your yard is an attractive three feet tall and it grows a foot per season, prune the branches back by a foot at least. It will maintain its natural shape as it matures during the summer.
What NOT to Prune in Spring
Forsythia, quince, mockorange, lilacs, and all the other beautiful spring bloomers should not be pruned until after they bloom. These early flowers are borne on old wood. Last season the buds formed after the shrub put on all of its growth, and the shrub has held on to the buds all winter long. If you prune during the shrub's spring dormancy, or, as in the case of my lovely quince, if the rabbits prune them all winter long, you will be cutting off this season's flowers. Instead, wait until the flowers have passed and then take the pruners to them. Lilacs in particular should be pruned as soon as they are finished blooming.
Yellow forsythia buds on last season's growth
Notice the forsythia buds on last season's growth - prune after blooming
Pink quince blooms on last season's growth
Likewise, quince blooms on last season's wood and should be pruned after flowering