There are many different types of shrubs, and their pruning needs differ greatly according to their growth habits. Some shrubs are dense with thin branching and a bushy growth habit. Others may have a graceful drooping habit with thicker arching branches. Certain shrubs have a more upright growth while others tend to spread out. How to prune your particular plant will depend a lot on your personal taste and the look you are going for in your landscape. There are, however, a few tried and fast rules to remember that will keep your shrubs healthy and looking their best.
Always immediately remove damaged, dead, and diseased branches for health reasons. This can be done any time of year and is often the first step in more extensive pruning. Most flowering shrubs are pruned after the flowers fade which often occurs in late spring or early summer. This is also good time to go ahead and consider the desired shape and size of your shrub and make necessary adjustments. Suckers also can be removed any time although some gardeners prefer to use suckers as a means to propagate new plants.
Technically, there are four kinds of pruning: pinching, shearing, heading, and thinning.
However, the first two don't actually involve pruners. Gardeners commonly "pinch" annuals, using thumb and forefinger, to keep them compact. Shearing is performed on hedges with shears (a larger tool than pruners) or a power hedger. Shrubs such as boxwoods (Buxus spp.) are ideal candidates. Of the remaining two procedures, thinning is more common, so let's take a close look at how to perform thinning cuts on a shrub.
What Is Heading vs. Thinning?
"Heading" means pruning off the terminal growth of a branch down to just above a lateral bud. This stimulates the buds right below the cut, resulting in denser growth. "Thinning" entails removing whole branches back to their point of origin. Here the goal isn't to stimulate denser growth but rather to shape, open up, or rejuvenate the shrub.
Many newbies lose out on optimal floral displays from shrubs that bloom in spring on old wood, such as quince (Chaenomeles speciosa) because they pruned too late the prior year (removing flower buds in the process). Prune this type of shrub right after the flowers begin to fade in mid-spring. The exception is when you're performing rejuvenation pruning, which is best done in late winter.
What Is Rejuvenation Pruning?
When a shrub gets old and its performance lags, rejuvenation pruning can revive it. The process occurs over a 3-year period. Each year, prune out 1/3 of the branches (right down to the ground), starting with the oldest 1/3 the first year. The second year, cut out another 1/3 of the oldest remaining branches. The third year, prune out the oldest branches left, leaving only the youngest, healthiest branches.
Prune shrubs that bloom in summer or fall on new wood, such as beautyberry (Callicarpa dichotoma), in late winter. Floral count for the current year won't be impacted.
Avoid pruning any shrub too late in the growing season, which encourages tender new growth that will die in winter.
Before Getting Started
Begin by deciding whether to use anvil or bypass pruners.
Of the two, bypass pruners are more like scissors, except that their blades are curved. When you squeeze the handles, these two blades "bypass" each other. The result is a sharp, clean cut. Achieving such a cut isn't just an aesthetic issue: Pathogens can gain entry into a branch more easily through messy cuts. Anvil pruners are designed differently. They're not curved. They're composed of one straight cutting blade and one flat edge (or "anvil"). When you squeeze the handles, the cutting blade closes down upon the anvil. Because of this crushing action, the quality of the cut differs from that of bypass pruners. Instead of receiving a sharp cut, the green wood of a living shrub branch tends to get a bit pulverized.
Anvil pruners are fine for removing dead wood, but bypass pruners are better for pruning living wood. That's one reason why we'll be using them here; that, plus the fact that anvil pruners are bulkier than bypass pruners, making it harder to get in close for crotch cuts.
Equipment / Tools
- Bypass pruners
- Gardening gloves
- Protective clothing
- Isopropyl alcohol
For our example of making a thinning cut, we'll use a spring-flowering shrub such as Forsythia, which should be pruned right after blooming is finished. Under the "thinning" umbrella are a number of possible pruning operations; We'll consider each one as we proceed through the project. You won't necessarily have to perform each of these operations every time you prune. Whenever you do decide to make one of these pruning cuts, remember that "thinning" means removing whole branches back to their point of origin. The point of origin can be the trunk, a larger branch, or ground level. Make your cut flush to the point of origin (don't leave stubs).
Some shrubs are more graceful than others. Quince's shape isn't graceful, but Forsythia bears a graceful shape by nature. Many prefer this natural form and feel that it can be spoiled by indiscriminate pruning. Err on the side of pruning less, not more, until you become more experienced.
Sterilize the Pruners
Sterilize your pruners with isopropyl alcohol before making any cuts just in case they're harboring pathogens.
Give the Shrub a Health Inspection
Inspect the shrub for damaged, dead, or diseased limbs, and prune these off first.
Inspect for Crossing Branches
See if any branch is rubbing up against another one. In each case, determine which branch you'd rather keep and remove the other. Such rubbing isn't healthy for the plant: The shrub's interior needs to be opened up.
Evaluate the Shrub's Shape
Are you happy with the overall form of the plant? If not, this is the time to make adjustments. If there's an odd branch shooting up crazily that you don't like, prune it off.
When to Do a Heading Pruning
Regardless of whether you are pruning to encourage branching by heading or pruning to thin and rejuvenate a plant, the above steps apply in both cases. Some shrubs that benefit from heading include rosebushes, ninebark, viburnum, and certain shrubby herbs like rosemary and lavender. Heading is done in mid to late winter and early spring to encourage new branching and flowering. If you want to increase branching in a shrub that blooms on old wood, make these pruning cuts as soon as the current season's flowers fade. You will be removing the terminal bud and a portion of the branch to just above a bud at a spot where you want a new branch to develop and fill in.
What to Do After Pruning
Keep a journal recording the performance of the plant from year to year, of how well your Forsythia blooms. When performance begins to lag, plan phase 1 of a rejuvenation pruning for late winter some year. You'll be sacrificing flowers for that year on behalf of superior future performance. Follow up with phases 2 and 3 in ensuing years.