Extension Master GardenerSM Volunteers of Buncombe County

pruning

Time to Maintain: How to Prune Summer-Flowering Shrubs

“No, I don’t think you killed your beautyberry,” I replied to a visitor to the Extension Master GardenerSM office concerned that their pruning efforts had irreparably damaged a favorite shrub. One of a Master Gardener volunteer’s most interesting challenges is reassuring people that nature is very resilient! This is particularly true when it comes to pruning, which many home gardeners look upon with a sense of dread. I reassure them that the worst that can happen is severely diminished flower production for next season—but there are no overall adverse effects on long-term plant health!

Beautyberry 'Issai'_K M_CC BY 2.0_Flickr
Beautyberry

As with most things involving gardening, there is an exception to this fact, which is to avoid pruning shrubs from mid-August until leaf fall. Late season pruning may encourage a flush of tender new growth that the onset of winter weather may kill back because it hasn’t had enough time to harden off. 

Summer-flowering shrubs
Glossy Abelia (Abelia grandiflora), summersweet (Clethra alnifolia), crape myrtle (Lagerstroemia indica), rose of Sharon (Hibiscus syriacus), old-fashioned Weigela (Weigela florida), American beautyberry (Callicarpa americana), New Jersey tea (Ceanothus americanus), and Virginia sweetspire (Itea virginica) bloom on new wood.  Botanically, these shrubs bloom on buds that develop on the growth that occurs in the spring of the current year. These species should be pruned in late winter or early spring (late March to early May) to promote vigorous growth early in the summer.

NOTE: We’ll discuss pruning hydrangeas in a future blog post. So, stay tuned!

What and when to prune
Does this mean you should put away your pruners now if you have summer-blooming shrubs? No, you can always remove damaged, dead, diseased, or double-crossed limbs (the “Four Ds”).  You can also remove spent flower heads, but this is done for cosmetic purposes—remove only the flower head, not any other part of the plant! 

Pruning techniques
When the time is right for pruning your summer-flowering shrubs, there are different approaches.

Rejuvenation is a drastic technique that works well on multi-stemmed, twiggy shrubs, and is typically done only every 3 to 5 years. It involves pruning all the stems back to about six inches above the ground. 

Selective pruning involves removing specific branches and limbs to improve the overall appearance of the shrub, shape the plant for landscape use, and reduce the overall height of the plant. Do not remove more than one-third of a plant’s growth in any one year except when you do rejuvenation pruning on a set schedule.

Don’t shear! Reserve shearing with electric or manual hedge trimmers for broadleaf evergreens—it is not appropriate for deciduous shrubs! 

Crape myrtle_improper pruning_CC BY 2.0_Flickr
Improperly pruned crape myrtle

Avoid “crape murder.” The drastic pruning of crape myrtles, commonly called “crape murder,” involves the wholesale reduction of the shrub’s height. This is equivalent to tree topping, which should not be undertaken under any circumstances! The result of such pruning is weakened structure and a reduction in vigor.

Article written by Bob Wardwell, Extension Master GardenerSM Volunteer.

More information
Pruning Trees & Shrubs: General Pruning Techniques
by Barbara Fair, Lucy Bradley, Anthony LeBude
Department of  Horticultural Science, NC State University

Time to Maintain: Winter Pruning of Crape Myrtle Trees
by Beth Leonard, Extension Master GardenerSM Volunteer

Time to Maintain: Pruning Conifers—Know Species Before Using Your Pruners

Conifers are plants that “set” seed-containing cones to reproduce, in contrast to plants that flower to form seed containers. If you equate “conifers” with “evergreens,” think again! Although many conifers are evergreen, the aptly named bald cypress (Taxodium distichum) is one example of a deciduous conifer that loses its needles in winter. Mountain laurel (Kalmia latifolia) is one of many evergreens that are not conifers. This is one reason correct identification of your plants is so important when you seek advice about your landscape!

American arborvitae cone_Maggie_CC BY-NC 2.0_Flickr
American arborvitae cone

Common conifers
Evergreen conifers commonly grown in our landscapes include Carolina hemlock (Tsuga caroliniana), Norway spruce (Picea abies), white pine (Pinus strobus), Eastern red cedar (Juniperus virginiana), American arborvitae (Thuja occidentalis), blue rug juniper (Juniperus horizontalis), hinoki falsecypress (Chamaecyparis obtusa), English yew (Taxus baccata), and Fraser fir (Abies fraseri). 

Amazing conifers
Conifers contain examples of the world’s oldest trees, such as the bristlecone pines (Pinus longaeva). These grow in the desert mountains of California and Nevada and are estimated to be over 5,000 years old. Many of the world’s biggest trees are also conifers. These include the giant sequoias (Sequoiadendron giganteum) found in the Sierra Nevada Mountains of California that can reach heights of 95 meters (312 feet), and the coast redwoods (Sequoia sempervirens) growing along the California coast that can reach heights of 110 meters (361 feet). 

Bald Cypress in Autumn_Lake Crabtree Park_Cary NC_by bobistraveling_CC BY 2.0_Flickr
Bald cypress in autumn, a deciduous conifer

Pruning
Before you make any decisions about pruning, consider the natural growth habit and landscape value of the plant. Most conifers require only minimal pruning and will perform well in your landscape without your intervention. That said, do not hesitate to get out your pruning tools when you see dead or diseased branches. Leaving these on a tree or shrub provides a route for disease pathogens and insects to enter and they should be promptly removed. Many gardeners choose conifers for formal or informal hedges. When you shear any conifer hedge, remember to leave the bottom of the plants a bit wider than the tops to get light to the lower limbs, keeping them lush and green.

Most conifers are “self-limbing.” They naturally lose their lower branches as they mature. Have you walked through a mature, healthy pine forest? You’ll see hardly any limbs within 3 meters (about 10 feet) of the ground. This is not the pruning work of some forest gnome! The trees shed their lower limbs on their own as they grow taller. This is an example of knowing the natural growth habit of your landscape plants when making pruning decisions. 

Different conifer species bud differently and therefore require different approaches to pruning.

  • Pines have buds only at the tip of the current season’s growth, not on the stems. So, prune pines in the spring when you can cut or pinch the soft new growth—called “candles”—before the needles are fully elongated. Buds will develop from needle sheaths below the cut.
  • Firs, cedars, and spruce also bud along the current season’s growth, but on the stems. Prune these species back to the bud before the current year’s growth hardens.
  • Yews and hemlocks bud on both old and new wood. Their buds develop into twigs when you cut the wood above. Pruning in the spring, just before the new growth begins, allows new growth to cover the pruning cuts.
  • Juniper and arborvitae have buds present only where there are green leaves. Note that prolonged use of electric hedge shears on juniper and arborvitae hedges will result in a very small veneer of needles just on the outer surface of the plants. If part of a continually sheared plant dies or is cut back too far, there are no inner leaf buds to develop, and you will be left with a “hole” in your hedge.

Remember, the Buncombe County Extension Master Gardener HelpLine and Information Tables are important sources of information about identifying and maintaining garden plants, including conifers.

Article written by Bob Wardwell, Extension Master GardenerSM Volunteer. 

More information
Selecting Landscape Plants: Conifers
by Virginia Cooperative Extension

The ConiferBase
by American Conifer Society
Online database provides information and photographs about conifers, including pruning, care, and varieties.

Time to Maintain: Pruning Spring-Blooming Shrubs

I answered the Garden Helpline in the Extension Master Gardener office recently and spoke to a very upset individual: “Why on earth, after all my hard work and attention, did my beautiful lilacs (Syringa vulgaris) not bloom this year?” I asked about growing conditions—full sun is needed for bloom—and watering and fertilizing, receiving all the correct answers. Then we talked about pruning: “It looked very scraggly and overgrown and I wanted to make it look nice for the spring, so I pruned it in February.” There was the answer to the question!

Lilac_Syringa vulgaris_F D Richards_CC BY-SA 2.0_Flickr
Lilac in bloom

Pruning time matters
Timing is critical, especially when pruning spring-blooming shrubs that develop their flower buds during the summer and fall of the previous year. This is often called “blooming on old wood.”

Plants, such as flowering quince (Chaenomeles speciosa), forsythia (Forsythia x intermedia), oakleaf hydrangea (Hydrangea quercifolia), bigleaf hydrangea (Hydrangea macrophylla), mountain laurel (Kalmia latifolia), azaleas and rhododendrons (Rhododendron spp.,), doublefile viburnum (Viburnum plicatum var. tomentosum), as well as lilac, are in this category.

While June 15 is often mentioned as a cut-off date for flowering time for “spring-blooming shrubs,” we gardeners know that Mother Nature does not always adhere to clear-cut time frames. What’s important is to correctly identify the plants and prune these shrubs soon after flowering. Pruning these shrubs in late summer, fall, or early spring will remove the flower buds—so pruning your lilac in February will remove the flower buds set last year!

Pruning soon after flowering means pruning no more than six weeks after this years’ blooms die. So even if your work or vacation time prevents you from getting to the task immediately, you still have time to prune and not adversely affect next years’ blooms. 

How to prune
The object of pruning is to open up the top of the plant to permit light and air to reach the interior. It can promote new plant growth, maintain plant size, encourage flowering, remove diseased or dead limbs, and help control insect and disease problems.

When thinking about pruning, consider the “one-third” rules: remove about one-third of the oldest wood at the ground level and cut back one-third of the younger, newer canes about one-third of their height per season.

The two basic types of pruning cuts are heading cuts and thinning cuts. Heading cuts remove part of the branch back to a bud. The direction in which the top remaining bud is pointed will determine the direction of the new growth. Selective heading cuts reduce the shrub’s height and retain its natural form.

Thinning cuts remove an entire limb to where it originates—in the case of shrubs, this could be at ground level. Thinning cuts remove the thickest, oldest stems with the fewest flowers. This opens up the canopy and increases light penetration and air circulation. To rejuvenate overgrown specimens with a suckering growth habit, such as forsythia and lilac, periodically removing the biggest, oldest stems at ground level allows new stems to replace the older ones.

An exception
If you have overgrown or unsightly spring-flowering shrubs, you may need to sacrifice one year’s bloom to get your garden looking good again. Renewal pruning is called for if you need to start over! In this case, prune the entire shrub back to 6 to 12 inches before your shrubs leaf out in the spring—either in late fall or early winter. Prune new growth lightly during the summer to get your shrub into shape for the future!

Article written by Bob Wardwell, Extension Master GardenerSM Volunteer.

More information:
Pruning Flowering Shrubs
by Elaine Fogerty, Agricultural Assistant
Rutgers Cooperative Extension
(Diagrams show different types of pruning cuts.)

Pruning Flowering Shrubs
Penn State Extension

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Buncombe County Extension Office
49 Mount Carmel Road
Asheville, NC 28806
Helpline 828-255-5522

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