Pruning and renewing native shrubs: when each kind is cut, and which never need it

A native shrub that blooms in spring is pruned right after it flowers, since next year’s flower buds form on the wood that grows this summer. A shrub that blooms in summer, on shoots of the same year, is pruned in late winter before growth starts. An old shrub of many stems is renewed by cutting its oldest stems at the ground, a few each year, and a few kinds take a cut of the whole clump. Most of the shrubs we grow need little pruning or none beyond dead wood.

Why most native shrubs need little pruning

A shrub left in its natural shape needs very little pruning, while one sheared or trained into a form needs frequent attention. Chosen for its full size and planted where that size fits, a shrub needs no cutting back to stay in bounds. One that outgrows its spot needs drastic pruning to hold its size, and stays a chore until it is replaced.

Many natives renew themselves as well. Bog spicebush needs no pruning, since root suckers replace the old stems in time. Red elderberry canes are short-lived, but the clump renews itself from suckers.

What is left for the pruners is short. Dead and broken wood can come off at any time of year. The rest is an old clump gone bare at the base, a shrub that has outgrown its space, and a hedge. A cut made for no reason does harm:

“When plants are pruned heavily or without a clear purpose in mind, they may end up being worse off than if they were left alone.” (University of New Hampshire Extension, The Basics of Pruning Trees and Shrubs)

When each kind is cut

Most of the shrubs we grow fall into one of five groups by when they are cut. The table names the commonly planted kinds in each group and counts the rest, and each shrub sits in one row:

How to tell old wood from new

NC State’s rule of thumb is that a shrub blooming before June blooms on old wood, and one blooming later blooms on new. The buds give a second test. Flower buds are larger than leaf buds, and on a shrub that blooms on old wood they sit on the twigs all winter. Wild hydrangea breaks the calendar rule, flowering from May on stems that grew that spring.

Shrubs with a season of their own

Bear oak, sandhill oak and the other shrub oaks are pruned only in winter, because oaks cut in spring draw the beetles that carry oak wilt. Witch hazel blooms from October into December and forms next fall’s buds in summer, so it is shaped, if at all, in early spring.

How a cut on a shrub differs from a cut on a tree

A branch thick enough to need a saw is cut as on a tree, just outside the collar, never flush and never leaving a stub, as pruning at the branch collar shows. Most shrub cuts are made in one of two other places:

• At the ground. A whole stem comes out at its base. The oldest stems are usually also the tallest, so taking them lowers the shrub the way it grew and lets light into the middle.
• Just above a bud. A shoot is shortened on a slight slant a quarter inch above a bud that faces outward, so the new shoot grows out and not into the crowd.

Thinning, which takes a stem back to the ground or to a side branch, is usually the better cut. Clipping the ends of every shoot, which is shearing, grows a dense shell of new shoots at the surface. Less light reaches inside, the inner leaves thin out, and the shrub turns stemmy and top-heavy.

Take no more than a third of a shrub in a year. Heavier cutting answers with a mass of vigorous new shoots, so hard pruning to keep a shrub small makes the problem worse. The kinds that regrow from a cut to the ground are the exception.

Renewing an old, bare-legged shrub

An old shrub of many stems that has gone bare at the base, flowering only at the top, is rebuilt from the ground up over three years:

1. The first late winter, before the buds break, cut a third of the stems at the ground, the oldest and thickest first.
2. The second late winter, cut half of the old stems that are left. Thin the new shoots to several strong, well-spaced ones, and cut out any thinner than a pencil.
3. The third late winter, take the last of the old stems. From then on, take a few of the oldest every two or three years.

On a shrub that blooms on last year’s wood, the same cuts can wait until just after it flowers, which keeps one more spring of bloom. The names differ by source: Iowa State and Clemson call the whole cut below renewal, while Minnesota’s extension and the Morton Arboretum keep that word for the gradual method above.

The whole cut takes every stem to 4 to 12 inches above the ground in late winter or early spring, before growth starts. It suits the kinds in the table’s fourth row. Five shrubs from other rows take it too, every few years or once they grow ragged: black elderberry, red osier dogwood, arrowwood viburnum, gray dogwood and buttonbush. A crowd of new shoots grows that season. The next late winter, keep several strong ones, cut the rest at the ground, and shorten the keepers so they branch.

A spring bloomer cut this way loses that spring’s flowers, a fair trade for an overgrown shrub:

“That season’s flowers may be sacrificed but the benefits from bringing the plants back to their normal size and shape outweigh this temporary collateral damage.” (University of Minnesota Extension, Pruning trees and shrubs)

Not every shrub can take this cut. A newly planted one waits until it has rooted in. Narrow-leaved evergreens such as junipers cannot grow new shoots from bare wood, so a hard cut leaves gaps that never fill.

What a cut at the wrong time costs

A spring bloomer cut in fall, winter or early spring loses the flower buds it set the summer before. The berries go with them, and a badly timed cut is one of the reasons a shrub bears no fruit. For spicebush and arrowwood it is a lost crop of fat-rich fruit for migrating birds.

Late summer and fall cuts carry a risk of their own. They can wake buds into soft growth that an early frost kills, and wounds made then die back more over winter.

Hard pruning harms some shrubs outright. Heavy pruning weakens northern bayberry and can cause dieback, so only its few lanky shoots are headed back.

A sheared hedge can lose its bottom. Trimmed narrower at the base than at the top, it loses its lower leaves and branches to the shade above, and the bare base spreads with age. The few natives that take the shears, and how to shape them, are in native hedges, screens and windbreaks. Sheared shrubs and hedges also tend to live shorter lives than unsheared ones.

Choosing a shrub that never needs cutting back

Blue Whale Trees grows every shrub in the table from seed, and the mature height on each plant page is the size to plan for. Three next steps:

• A shrub that stays in bounds: the tree finder lists the shrubs we grow that top out at 15 feet or less, by your zone, sun and soil.
• A shrub already in the ground: the growing guide on each plant page holds the timing for that kind, and the table above gives its group.
• A cut in doubt: write to us before you cut; a photograph of the whole shrub and its base can follow by email once we reply.

Common questions

When should I prune spicebush?

Right after its early spring bloom, and only if it needs shaping, since it flowers on old wood. A winter cut takes that spring’s flowers and, on a female plant, the red berries of late summer.

When do you prune viburnums?

Right after they flower, since next year’s flowers form on old wood, and that holds for arrowwood, blackhaw, nannyberry and mapleleaf viburnum. A leggy arrowwood can instead be cut to the ground in late winter.

When should elderberry be pruned?

From its third winter on, black elderberry loses its dead canes and any cane older than three years, or the whole bush is cut to the ground every few years. Red elderberry flowers on last year’s wood, so a late-winter cut costs its bloom.

Can I prune shrubs in the fall?

Only dead or broken wood, which can come off at any time of year. Fall cuts die back more over winter and can wake soft growth that frost kills, so the rest waits for late winter or the end of bloom.