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Pruning Ornamental Shrubs and Vines

By Neil Bell Community Horticulturist Marion and Polk Counties

What is pruning?

Timing of pruning

Pruning principles

Specific pruning techniques:

Shrubs Conifers Vines

Why prune?

Frequency of pruning

Pruning references

Contents:

What is Pruning? The selective removal of specific parts of the plant to benefit the whole plant

Corylus avellana ‘Contorta’

Pruning is NOT: a way to compensate for inappropriate plant placement!

Plant placement

Consider the mature size of plants and available space

A couple of exceptions…

Coppicing Subshrubs

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Why Prune? Develop unusual forms

Remove dead, diseased or broken parts

Prune out winter injury

Removal of reverted growths

Euonymus

Buxus

Sucker removal

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Shape the plant: directing growth

Rosa ‘Eddie’s Jewel’

Size Control: short term only!

Why Prune at all?

Pruning is a stress on plants

March June

is that really desirable?

Plant will grow unassisted to natural form

Timing of Pruning

1. Flowering habit

Blossoms on old wood Blossoms on new wood

Depends on:

Viburnum plicatum Phygelius

2. Objectives remove dead wood anytime

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3. Risk of winter injury Fuchsia, Hebe, Salvia etc.

Salvia desoleana

4. Convenience…

Philadelphus lewisii

Frequency of Pruning

1. Prune only as needed

Growth habit will influence pruning requirement

2. Type of plant clipped hedges

3. Need for size control maybe not practical!

Know the plant and keep a good reference around…

Witch hazel (Hamamelis x intermedia)

observe growth/flowering

observe the response to cuts

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Most importantly: learn what your pruning will do! Principles of Pruning

Directing growth

Adaptations to damage and disease

Growth of woody plants

Principal pruning cuts

Growth habit of woody plants

Lilac: Syringa vulgaris Spring 2014

Growth resumes at shoot tip

Not all buds develop

Twig diameter increases with age

2013

2012

2011

2010

2009 Shoot length decreases yearly

color change in wood

Flowering currant: Ribes sanguineum

Terminal Bud (auxin)

Axillary Bud

Flower Bud

Latent Bud

Parts of a branch

Node

Cherry Laurel (Prunus laurocerasus)

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Flower buds/flowers/fruit are for one season only…

Serviceberry (Saskatoon): Amelanchier alnifolia

Vegetative buds live indefinitely…

450 angle

Good!

Too angular Too low Too high

Directing growth:

Alternate-budded plants Opposite

Cutting above a bud

Response to pruning

removing terminal bud

allows lateral development

topmost remaining bud grows most strongly

alternate opposite

removal of material causes growth elsewhere

Another way to force branching… Cutting back branches

Cut back always to a part that will continue to grow

At least ½ the size of the part being removed

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Pruning cuts Thinning removal of entire stem or section of stem

opens up the plant to admit light

reduces overall height and promotes regrowth

Thinning cut

Philadelphus lewisii

Heading (selective)

Cutting back to a bud or shoot

Promotes branching, will “fill in” the plant

Heading cut

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Shearing

Non-selective heading: dense growth at branch tips

Unnatural form, appropriate for formal hedges

Thinning

Heading

Pinching

Heading, Thinning and “Pinching”

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Enhance a characteristic: Coppicing

Shrub dogwood (Cornus sanguinea) C. sanguinea ‘Midwinter Fire’

Annual hard pruning preserves cane color, reduces size

Coppicing:from the French “to cut”

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Coppicing to enhance leaf size… Cotinus coggygria (smokebush)

Renovation

Cutting all canes back to near base to renew all growth

Very harsh technique: not appropriate for all plants!

February, 2009

April, 2009

January, 2010

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Adaptations to damage and disease

Plants have no “wound healing” process: healing in a sense of replacing or repairing injured tissues.

Plants seal off damaged tissue rather than heal it.

CODIT Compartmentalization Of Decay In Trees

Plants are highly ordered, compartmented Instead of healing, plants compartmentalize

injured and infected tissues.

callus tissue is produced on the wound margin Wound paints and dressings

evidence for use is inconclusive

no given treatment fulfills all requirements

1. Prevent decay

2. Speed wound closure

3. Inhibit insect or diseases

http://pnwhandbooks.org/plantdisease/pesticide-articles/tree-wound-paints

Further reading from the PNW Disease Management Handbook:

When and how to prune a shrub depends on…

1. Flowering habit 2. Growth habit

Calycanthus x raulstonii

Pruning Shrubs

Rosa sp.

1. Blooms on “old” wood:

Determining time to prune flowering shrubs The “flowering habit”

2. Blooms on “new” wood:

The issue is:

When does the shrub form the flower buds?

after flowering

early spring

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Flowering Quince (Chaenomeles sp.)

Spring blooming shrubs develop buds in fall Tend to bloom early in season

Distinguishing between “old” and “new” wood Summer/fall blooming shrubs form buds as they grow Tend to bloom later in season

Japanese Spiraea (Spiraea japonica)

Stachyurus praecox ‘Variegata’

“Current season” versus “previous season” growth Length of bloom period

Rhododendron

Spring bloomers: 2 weeks?

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Fuchsia magellanica

Summer bloomers: often more than a month Flower type: terminal or axillary

Fuchsia-flowered gooseberry (Ribes speciosum)

Axillary

Terminal flowers

Hydrangea paniculata

Terminal flowers: Current season wood i.e. Buddleja (July-September)

Lateral flowers: One year-old wood i.e Chaenomeles (February-May)

“New” wood versus “old” wood

Some shrubs cause confusion!

Hydrangea macrophylla Hydrangea macrophylla Endless Summer™

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Genera with species that flower

on both new and old wood

Rosa

New: Repeat bloomers

Old: Once-blooming, species

Hydrangea New: H. paniculata, H. arborescens

Old: H. macrophylla

Spiraea New: S. japonica, S. ‘Bumalda’

Old: S. x vanhouttei, S. ‘Arguta’

How to prune: depends on growth habit

Cane growers: i.e. Philadelphus

Permanent framework: i.e. Rhododendron Subshrub: i.e Perovskia

Cane growers are easy to identify

Hydrangea macrophylla

Cane growers

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Deutzia sp.

“Cane” growers

Deutzia Forsythia Hydrangea (Mophead etc.) Kolkwitzia (Beautybush) Philadelphus (Mock orange) Physocarpus (Ninebark) Ribes (Currant/Gooseberry) Sambucus (Elderberry) Spiraea (“Bridal Wreath”) Rosa (Rose) Viburnum Weigela

Permanent framework

Have a “tree-like” structure

Do not renew themselves from the base Often are evergreen shrubs

Pieris japonica Rosmarinus officinalis ‘Arp’

Permanent Framework

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Hebe ‘Red Edge’

Arctostaphylos (Manzanita) Ceanothus (Wild lilac) Cistus (Rockrose) Daphne Hamamelis (Witchhazel) Hebe Hibiscus (Rose of Sharon) Ilex (Holly) Lavandula (Lavender) Pieris (Andromeda) Rhododendron (and azalea) Rosmarinus (Rosemary)

Permanent Framework

Arctostaphylos catalinae

Some are deciduous…

Hamamelis (witchhazel)

Hibiscus syriacus (Rose of Sharon)

Subshrubs

Salvia microphylla Phygelius ‘Sensation’

Have a woody framework Produce flowers on new growth

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Artemesia sp.

Vitex agnus-castus

Artemisia (Wormwood) Caryopteris (Bluebeard) Ceratostigma (Plumbago) Fuchsia magellanica (etc) Gaura lindheimeri Heptacodium (7 Sons Plant) Hydrangea paniculata Lavatera (Tree mallow) Salvia (Sage) Perovskia (Russian sage) Penstemon Phygelius (Cape Fuchsia) Vitex (Chaste tree) Zaushneria (California Fuchsia)

Some examples of subshrubs

Lavatera spp.

Pruning Cane growers

Deutzia ‘Pride of Rochester’

Remove: • dead • damaged • crossing • twiggy growth

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Year 1 Year 2 Year 3 Deutzia ‘Pride of Rochester’

Deutzia scabra “Limbing up”

Shearing cane growers

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Few flowers!

Effects of topping canes (i.e. heading)

Viburnum opulus

February April