When it comes to growing flowering shrubs, it’s important to know how and when to properly prune them. Flowering shrubs bloom at different times, and therefore not all shrubs should be pruned at the same time. Fortunately, the majority of flowering shrubs fall into two categories that determine how best to prune them: shrubs that bloom on old wood and shrubs that bloom on new wood.
Should you Prune Flowering Shrubs?
In short, yes! Deciduous shrubs that grow in temperate climates (those with cold winters) may benefit from occasional pruning, or sometimes become unruly and need to be pruned back to a manageable garden size. But when you should prune your shrubs can depend on the shrub’s size, health and bloom period, as well as the time of year.
When to Prune Flowering Shrubs? Old Wood vs. New Wood
Different shrubs have different growth patterns, and it matters when in their growth cycle you prune them. Some shrubs produce flowering buds on their previous year’s growth, commonly called “Old Wood,” while others flower on their current year’s growth, or “New Wood.” Some will also produce flowers on both their old and new growth. A general rule of thumb is that most early Spring blooming shrubs bloom on old-wood, while new-wood shrubs flower later in the season and often for longer.
So when do you prune them?
Spring Flowering Shrubs | Summer/Fall Flowering Shrubs |
| Spring flowering shrubs or spring blooming shrubs can be pruned in the spring after they have flowered. Most of these are “Old Wood” and can be cut after the blooms open. | Summer or fall flowering shrubs can be pruned in the early Spring if desired. Many reblooming shrubs, like many Roses, benefit from additional deadheading throughout the season. |
How to Prune Flowering Shrubs
Pruning needs will vary from shrub to shrub. Not all shrubs need to be pruned, and some only occasionally. If you want to prune a shrub to either control or reinvigorate its growth, it’s best to follow the Old Wood vs. New Wood schedules. Here are some general guidelines for how and what to prune your flowering shrubs:
Renewal Pruning: Pruning out long, overgrown or dense branching to reshape and expose branches to more sunlight and airflow is called renewal pruning. This type of pruning in turn helps prevent diseases. This can be especially important for fruiting shrubs such as Serviceberry, Chokeberry, or Bush Cherries, but will also help plants flower better or grow more uniformly. Most shrubs can be thinned out this way on a yearly basis.
Rejuvenation Pruning: When shrubs become overgrown or unruly, you can often prune them back quite heavily to reinvigorate them. The best time to do this kind of pruning is in the early Spring, so that the plant has the entire growing season to recover and put on new growth. Bear in mind that for old wood shrubs, this process will remove flowering branches for that year.
You can also prune the “Four Ds” anytime: Dead, Damaged, Diseased, and Disorderly branches.
- Dead, hanging or damaged branches – These either contribute nothing to a shrub’s health and flower production or can be vectors for fungus, bacteria or pests to further compromise a plant’s health.
- Diseased branches – Branches with obvious disease or pest infestations should be removed. If there is a large or concerning problem, you may need to treat the shrub before it blooms.
- Crossing or rubbing branches – Branches that are too close to each other will crowd out healthy growth. Branches that rub against each other can cause damage and allow pathogens to enter.
Most Common/Types of Flowering Shrubs in Utah
Flowering Shrubs are favorites for Utah gardeners because they add beauty and structure to landscapes. Lilacs, Forsythias, and Viburnums are common all over Northern Utah because they are easy to grow even in tough soils. Rose bushes are another classic shrub for our area because they can handle heat, poor soil, and even salty, secondary water from Utah Lake.
Shrubs that Bloom on Old Wood
Many of our favorite Spring-blooming shrubs are old wood blooming. That means you’ll want to prune the following shortly after they bloom:
Forsythia: As one of the earliest-blooming shrubs in the landscape, bright yellow Forsythia flowers announce the coming of Spring. These shrubs bloom on old wood growth and should be pruned in the month after flowering. Pruning too late in the Summer or Fall will reduce the amount of blooming branches you’ll have next Spring.
Lilac: These old-school garden favorites provide profuse clusters of fragrant flowers in mid-Spring. But if you prune them in the Summer, Fall, or early Spring, you will be cutting off their blooming branches for the following season.
When to prune Lilacs: Both Common European and Dwarf Korean Lilacs fall into the old wood grouping and should be pruned within 2-3 weeks of blooming. Bloomerang Reblooming varieties, though, bloom on old wood in the Spring, and rebloom on new wood in the Fall. If desired, you can prune reblooming varieties within 2-3 weeks after their initial Spring bloom without compromising their Fall flowers. This applies to shrub forms as well as patio trees.
Viburnums: The genus Viburnum contains over a dozen species of shrubs that are used in landscaping, from ever-popular Snowball Bush Viburnum to the wonderfully fragrant Korean Spice Viburnum. All of the common viburnums are old wood blooming, and should be pruned within the month after flowering.
Other old wood flowering shrubs:
- Flowering Almond
- Flowering Currant
- Flowering Quince
- Beautybush
- Purple Sand Cherry (Cistena Plum)
- Chokeberry
- Cotoneaster
- Deutzia
- Dogwood
- Fothergilla
- Ninebark
- Privet
- Spiraea – Spring-flowering
- Sweetspire
- Weigela
- Witch Hazel
Shrubs that Bloom on New Wood
Many shrubs that flower from late spring to summer or through the fall produce flowers on their current year’s growth as opposed to the previous year’s. This often correlates to longer bloom times through the hotter months of the year. Some plants, such as Roses and Butterfly Bush, may produce more flowers if you prune them (deadhead) throughout their bloom cycle.
The following plants bloom on new wood and benefit from rejuvenation pruning in the early Spring:
- Bluebeard
- Butterfly Bush
- Dogwood
- Lavender
- Roses
- Russian Sage
- St. John’s Wort (Hypericum)
Other plants that bloom on new wood:
- Beautyberry
- Chaste Tree (Vitex)
- Chitalpa
- Diervilla
- Potentilla
- Rose of Sharon
- Snowberry/Coralberry
- Spiraea – Japanese varieties
- Summersweet (Clethra)
When should you prune Hydrangeas?
Pruning hydrangeas is dependent on what species of hydrangea you’re growing. Some are old wood bloomers and others are bloom on new wood. Head on over to our Hydrangea Pruning Blog to learn more about when to prune different kinds of hydrangeas.
FAQ About Pruning Flowering Shrubs
Can I trim a shrub or bush that is budding?
Yes, you can trim a shrub that has buds on it. In fact, many gardeners cut branches of Forsythia, Flowering Quince, or other Spring-blooming shrubs for flower arrangements.While you can trim a shrub that has buds on it, bear in mind that you’re removing those flowers from the shrub itself.
What is the 1/3 rule for pruning shrubs?
The 1/3 rule for pruning shrubs refers to the guideline that you should not cut more than 1/3 of a tree or shrub’s healthy, living branches at one time. Although a plant will heal from them, pruning cuts are a form of stress that can weaken a plant’s defenses and can make it more susceptible to pests or diseases while recovering. Ideally, you should pace out substantial pruning events over a few years to allow the tree to recover. The exception to this rule is renewal pruning, where you prune a shrub back more than ⅓ so as to drastically alter its shape and size.
How can I prune shrubs for more flowers?
If your shrub produces fewer flowers or stopped flowering altogether, there are a few things you can do. If your shrub has become crowded with branches that no longer flower, you can prune them out to expose newer branches to more sunlight and airflow. This type of pruning is called ‘Renewal Pruning.’ You can also prune down the shrub to a smaller size to encourage newer, healthier growth in a process called ‘Rejuvenation Pruning.’
What shrubs should not be trimmed?
It is not necessary to prune shrubs every year. Some shrubs don’t need to be trimmed very often. Many dwarf shrubs have a natural, compact habit and don’t need to be pruned to keep their shape. Avoid trimming any shrubs in the late Fall or Winter as this can result in frost damage.
What are common pruning mistakes?
A common pruning mistake is doing it at the wrong time of year. Make sure that you know what shrub you’re working with and whether it blooms on old wood or new wood. This will determine when the best time to prune will be. Other common mistakes are pruning too much of a shrub at one time, or making improper pruning cuts that can damage a tree.
How far back can you cut a shrub (bush) without killing it?
A general guideline for how much you can cut a shrub without killing it is the 1/3 rule. You should aim to not cut a shrub back more than 1/3 in a single season. Some resilient shrubs can handle more extensive pruning than others, but any deeper pruning should be done in the Spring so that the shrub has enough time to recover through the growing season.
