Extension Master GardenerSM Volunteers of Buncombe County

pruning

Time to Maintain: How to Prune Hydrangeas

Walking amidst “Munchkin,” “Ruby Slippers,” and “Snow Queen” at a local plant nursery, I wondered if I had wandered into some magical land “over the rainbow.” I was in the section of the nursery dedicated to hydrangeas!

Hydrangeas_Shinji W_CC BY 2.0_Flickr
Hydrangeas – a rainbow of color

Hydrangeas include more than 75 species of evergreen or deciduous shrubs native from Asia to North America. They are widely grown, relatively pest free, and require minimal annual maintenance. Consider including them in your landscape design—they will bring you multi-season enjoyment. 

Hydrangeas in North Carolina
The most common species of hydrangeas found in North Carolina landscapes are:

  • Bigleaf hydrangeas (Hydrangea macrophylla) come in two flower types: lacecap and mophead. If you adjust soil pH, you can modify their bloom color. They will bloom blue in acid (below 6) pH soil and pink in high (above 7) pH soil. This is a function of aluminum availability. White bigleaf hydrangeas will not change color with soil pH. There are over 1,000 cultivars of this species—some recent introductions may re-bloom on new wood. In Western North Carolina most bloom from June to August.
  • Mountain hydrangeas (Hydrangea serrata) also come in both lacecap and mophead flower types. They grow 2 to 5 feet high and 4 to 6 feet wide. There are over 100 cultivars. They are native to Asia, not our mountains, and bloom in May.
  • Oakleaf hydrangeas (Hydrangea quercifolia) grow 4 to 8 feet high and wide and are one of the hydrangeas native to the southeastern states. They flower in June with blooms lasting three to four weeks. Leave the spent bloom heads on the plants to add winter interest to the garden.
  • Smooth hydrangeas (Hydrangea arborescens) are native to our area and grow 3 to 5 feet high and wide. Flowers appear in June and last 3 to 4 weeks.
  • Peegee hydrangeas (Hydrangea paniculata) grow 15 to 25 feet high and 10 to 20 feet wide, if left unpruned. Their flowers open white from June through August.
  • Climbing hydrangeas (Hydrangea anomala subsp. petiolaris) are vines that can grow 60 to 80 feet tall if left untrimmed. Asian natives, they are slow to establish, but you will enjoy their ability to climb just about any vertical surface. Bloom time is late June to early July.

 Pruning care

  • Hydrangea macrophylla, H. serrata, and H. quercifolia bloom on old (last year’s) wood—prune after flowering. You can trim to shape them to fit into your landscape design. Remove dead, diseased, and damaged limbs at any time.
  • Hydrangea arborescens and H. paniculata bloom on new wood—prune in late winter (February to early March). They benefit from being cut back to six inches off the ground (i.e., rejuvenation pruning). Promptly remove all old, dead, diseased, and damaged stems.
  • Hydrangea anomala subsp. petiolaris requires very little pruning—train to grow this climbing hydrangea on its support surface. 

Article written by Bob Wardwell, Extension Master GardenerSM Volunteer.

Learn more
It’s All in the Soil! The Chemistry Behind Hydrangea Colors
YouTube video from the American Scientist

Prune hydrangeas at the wrong time and you snip off the season’s blooms.
by Glenn Palmer, Buncombe County Extension Master GardenerSM Volunteer

Smooth and Oakleaf Hydrangeas
by Ervin Evans and Richard E. Bir
Horticultural Science, NC State Extension

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.

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

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