It's the time of the year where you're probably starting to think about tidying up wayward shrubs and pruning hedges during the spring growth spurt. But before you grab shears or gas-powered hedge trimmers, let's talk about proper pruning practices and how they differ from species to species. Not all shrubs can be pruned the same if you want them to live long and prosper.
Rule #1 is to put away your electric or gas-powered hedge trimmers. Unless you're maintaining a substantial yew hedge or something like that, this tool doesn't have a place in shrub pruning. They can be useful for cutting back ornamental grasses or other sturdy perennials, but when used on shrubs they can tear and tatter twigs ends and leave the shrub vulnerable to pest and disease problems, along with leaving unsightly dead tips on branches.
Even if you're using sharp, clean hand shears, a tight globe or box look is not suitable for every shrub in the landscape. For some species, this kind of pruning can result in poor internal structure that leaves huge holes in the shrub if even a single branch is lost. Pruning shrubs into uniform shapes can also rob them of the beauty of their natural form. We pick shrubs not just to provide a desired flower color or fill a space; when we design we take into account the natural shape and texture of a shrub, and if you shear a shrub that isn’t meant to be sheared, you’ll lose its natural beauty. You can also be giving yourself a headache, as some species will fight back with aggressive shoot growth after shearing. If you've ever tried to shear forsythia, you know what I'm talking about.
However, there are times when you want or need the clean formal shapes that a pair of hedge clippers can bring. The following species tolerate shearing well: arborvitae, yew, boxwood, privet*, barberry*, and burning bush*. When shearing a hedge, keep the top slightly narrower than the base. Hedges that are narrower at the bottom often end up thin and scraggly at the bottom because sunlight can't reach the lower branches.
So how do you keep other species of shrubs in check if shearing isn't an option? Selective pruning is the process of removing individual branches to control the size and shape of your shrub or promote without destroying its natural shape. Branches can be cut back where they connect to a larger branch or snipped off just above a lower bud. If it seems like the bush is getting too dense and crowded, limbs can be removed all the way down to the ground. Make sure you look twice and cut once so you don't accidentally remove a limb that will leave a bare spot. This may be unavoidable at first if you're switching from shearing to selective pruning, but with time it will be easier. See the diagram on the left for an illustration of selective pruning.
If this seems like a lot of work, don't worry. Once you ditch the shears and pick up the hand pruners, you'll notice that your shrubs need considerably less taming. You will rarely see long, leggy shoots springing up left and right once you switch your methods and stick to it. Instead you'll just be removing the occasional wayward shoot and periodically reducing the shrub's size. If your shrubs have been sheared for so long that you are left with dense growth on the outer few inches and twiggy, leafless growth on the inside, then you may need to resort to renewal or rejuvenation pruning to bring it back to a healthy habit.
One last consideration in pruning is timing. Pruning should be done when the plant has the most time to recover, such as early spring or early summer (unless you're cutting just a few stems - you can do that any time without doing the plant any real harm). If you prune in the hottest part of the summer when your shrub is already stressed, you can increase the plant's stress and make it more vulnerable to other problems. Pruning in the fall can encourage new growth that won't have enough time to mature before freezing temperatures arrive, especially if you're shearing a hedge. Flowering shrubs need to be pruned at different times of year depending on when they flower. Spring blooming shrubs usually develop next year's flower buds during the summer, so it's vital that you prune immediately after flowering so you don't remove next year's flower buds. Summer blooming shrubs usually bloom on new growth, so they should be pruned after flowering, but before new growth starts in spring. Some shrubs can be pruned at any time, because they bloom on both new and old stems. Below I've listed some common flowering shrubs by optimum pruning time.
Prune in spring immediately after flowering:
Deutzia (Deutzia gracilis)
Forsythia (Forsythia x intermedia)
Rhododendron and Azalea (Rhododendron species)
Thunberg Spirea (Spiraea thunbergii) (varieties include 'Ogon')
Lilac (Syringa species)
Viburnum (Viburnum species)
Weigela (Weigela hybrids)
Dwarf Fothergilla (Fothergilla x gardenii)
Chokeberry (Aronia arbutifolia and melanocarpa)
Red Twig Dogwood (Cornus sericea)
Oak Leaf Hydrangea (Hydrangea quercifolia)
Big Leaf Hydrangea (Hydrangea macrophylla)
Prune before spring growth:
Butterfly Bush (Buddleia hybrids and species)
Beautyberry (Callicarpa species and hybrids)
Smooth Hydrangea (Hydrangea arborescens, varieties include 'Annabelle', 'Incrediball', 'Invincibelle Spirit')
Hardy Hydrangea (Hydrangea paniculata, varieties include 'Limelight', 'Pinky Winky', 'Quick Fire')
Sumac (Rhus species)
Virginia Sweetspire (Itea virginica)
Summersweet Clethra (Clethra alnifolia)
Bumald Spirea (Spiraea x bumalda, varieties include 'Anthony Waterer')
Winterberry (Ilex verticillata)
Prune before or after blooming:
Reblooming Hydrangeas (Hydrangea macrophylla, specific varieties such as Endless Summer series)
Knock-Out Roses (Rosa Knock-Out hybrids)
Japanese Spirea (Spiraea japonica, varieties include 'Little Princess', 'Goldflame', 'Magic Carpet')
I've provided some additional resources on pruning shrubs below. Feel free to direct any other questions you may have to me. Good pruning practices are essential to the long-term health and beauty of your garden, and we’d like to help. Contact us to learn more about what our maintenance team can do for you.
*Privet, barberry, and burning bush are considered invasive and should be avoided. Privet and barberry are included in Indiana’s newly adopted list of banned invasive plants, and they will not be available for purchase within a few years.