Pruning Ornamental Shrubs Contents: What is pruning? Pruning principles Growth of woody plants Group exercise: Identification of plant parts Pruning principles Directing growth Principal pruning cuts
Identifying flowering and growth habit By Neil Bell Community Horticulturist Pruning references Marion and Polk Counties Group exercise: Pruning problem worksheets
What is Pruning?
The selective removal of specific parts of the plant to benefit the whole plant
Witch Hazel: Hamamelis x intermedia
Forsythia sp.
1 Pruning is NOT: a way to compensate for inappropriate plant placement!
Plant placement There is an exception… Consider the mature size of plants and available space
PanicleSmooth Hydrangea: Hydrangea: Hydrangea Hydrangea paniculata arborescens Pinky ‘Annabelle’ Winky®
Principles of Pruning Growth habit of woody plants 2018
Lilac: Syringa vulgaris Spring 2019 Growth of woody plants 2017
2016 Directing growth
2015 Growth resumes at shoot tip Principal pruning cuts Not all buds develop
Shoot length decreases yearly 2014 Twig diameter increases with age
2 color change in wood
Flowering currant: Ribes sanguineum
“Current season” versus “previous season” growth Parts of a branch Terminal Bud (auxin)
Axillary Bud Node
Flower Bud
Latent Bud
Stachyurus praecox ‘Variegata’
Growth occurs from buds: vegetative or flower
Rhododendron: Rhododendron sp.
3 Vegetative buds live (more or less) indefinitely Flower buds/flowers/fruit are for one season only…
Serviceberry (Saskatoon): Amelanchier alnifolia
Boxwood: Buxus ‘Vardar Valley’ Wintersweet: Chimonanthus praecox
Bay Laurel: Laurus nobilis Flowering currant: Ribes sanguineum
4 Winter-flowering Honeysuckle: Lonicera x purpusii Chaparral Currant: Ribes malvaceum
Sweetbox: Sarcococca hookeriana February Daphne: Daphne odora
Spiraea: Spiraea thunbergii ‘Fujino Pink’ Evergreen Huckleberry: Vaccinium ovatum
5 Directing growth: Response to pruning Cutting above a bud
removing terminal bud allows lateral development
0 topmost remaining bud(s) 45 angle Too angular Too low Too high grows most strongly Good! Alternate-budded plants Opposite alternate opposite
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
Pruning cuts Thinning removal of entire stem or section of stem opens up the plant to admit light reduces overall height and promotes regrowth
6 Thinning cut
Philadelphus lewisii
Heading (selective) Heading cut
Cutting back to a bud or shoot
Promotes branching, will “fill in” the plant
7 Shearing
Non-selective heading: dense growth at branch tips
Appropriate for formal hedges
Privet: Ligustrum sp.
Port Orford Cedar: Chamaecyparis lawsoniana Atlas Blue Cedar: Cedrus atlantica
Heading, Thinning and “Pinching” Pruning Shrubs When and how to prune a shrub depends on… 1. Flowering habit 2. Growth habit Thinning
Heading
Calycanthus x raulstonii Forsythia x intermedia
8 Determining time to prune flowering shrubs The “flowering habit” 1. Blooms on “old” wood: after flowering 2. Blooms on “new” wood: early spring
The issue is: When does the shrub form the flower buds?
Distinguishing between “old” and “new” wood Spring blooming shrubs develop buds in fall Tend to bloom early in season
Flowering Quince: Chaenomeles sp.
Summer/fall blooming shrubs form buds as they grow Length of bloom period Tend to bloom later in season Spring bloomers: 2 weeks?
Japanese Spiraea: Spiraea japonica Rhododendron
9 Summer bloomers: often more than a month Flower type: terminal or axillary Axillary
Hardy Fuchsia: Fuchsia magellanica Fuchsia-flowered gooseberry: Ribes speciosum
Terminal flowers
Hydrangea paniculata Spiraea thunbergii ‘Fujino Pink’
“New” wood versus “old” wood
i.e. Buddleja • May-October • Long bloom time • Terminal flowers = Current season wood
i.e Chaenomeles • November-May • Short bloom time • Axillary flowers Hypericum sp. = Previous season wood
10 Berberis x lologensis Chinese Abelia: Abelia chinensis
Some shrubs cause confusion!
Hydrangea macrophylla Endless Summer™ Mophead Hydrangea: Hydrangea macrophylla
Genera with species that flower How to prune: depends on growth habit on both new and old wood CaneSubshrub:Permanent growers: framework: i.e.i.ei.e. Perovskia PhiladelphusRhododendron New: Repeat bloomers Rosa Old: Once-blooming, species
New: H. paniculata, H. arborescens Hydrangea Old: H. macrophylla
New: S. japonica, S. ‘Bumalda’ Spiraea Old: S. x vanhouttei, S. ‘Arguta’
11 Cane growers are easy to identify
Hydrangea macrophylla
Cane growers
“Cane” growers Deutzia Forsythia Hydrangea (Mophead etc.) Kolkwitzia (Beautybush) Philadelphus (Mock orange) Physocarpus (Ninebark) Ribes (Currant/Gooseberry) Sambucus (Elderberry) Spiraea (“Bridal Wreath”) Rosa (Rose: shrub types) Viburnum Weigela
Deutzia sp.
12 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
Hebe ‘Red Edge’
Permanent Framework
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) Arctostaphylos catalinae
13 Some are deciduous… Subshrubs
Rose of Sharon: Hibiscus syriacus Salvia microphylla Phygelius capensis Witch Hazel: Hamamelis
Have a woody framework Produce flowers on new growth
Artemesia sp. Vitex agnus-castus
14 Some examples of subshrubs Pruning Cane growers Artemisia (Wormwood) Caryopteris (Bluebeard) Epilobium canum (CA Fuchsia) Fuchsia magellanica (etc.) Remove: Gaura lindheimeri (Windflower) • dead Heptacodium (7 Sons Plant) • damaged Hydrangea paniculata • crossing Lavatera (Tree mallow) • twiggy growth Salvia (Sage) Perovskia (Russian sage) Penstemon (woody types) Phygelius (Cape Fuchsia) Rosa (repeat-flowering shrubs) Deutzia ‘Pride of Rochester’ Lavatera spp. Vitex (Chaste tree)
Year 1 Year 2 Year 3
Deutzia ‘Pride of Rochester’
15 “Limbing up”
Fuzzy Deutzia: Deutzia scabra Snowball Bush: Viburnum opulus
Over-thinning (and topping) Shearing cane growers
Snowball Bush: Viburnum opulus
Japanese Barberry: Berberis thunbergii Forsythia: Forsythia x intermedia
Effects of topping canes (i.e. heading)
Snowball Bush: Viburnum opulus
Few flowers!
16 February April
17 Pruning permanent framework Many of these plants form a dome-shaped canopy
Generally assume regular shape
Ceanothus ‘Julia Phelps’ Pieris ‘Valley Valentine’
Remove dead or damaged growth
Lavender Lavandula spp.
Rockrose: Cistus x argenteus ‘Silver Pink’
Removal of errant shoots help shape
1 “Cubist” pruning is common… Or the meatball variation…
Tea tree: Leptospermum sp. Arctostaphylos ‘Lusko’s Pink’
2 Think about flowering time before pruning!
Rosemary: Rosmarinus officinalis
Escallonia: Escallonia sp. Rhododendron sp.
Pruning subshrubs
avoid pruning until after risk of severe freeze
Salvia desoleana
3 Small subshrubs which may be sheared: Remove most shoot growth to base
California Fuchsia:Epilobium canum
Pineleaf Beardtongue: Penstemon pinifolius AugustJanuary 2010 2011
After… Salvia desoleana
Larger subshrubs…
Hypericum sp. Spiraea
4 Large subshrubs
SevenButterfly Sons Bush: Flower: Buddleia Heptacodium‘Pink Delight’ miconioides
Remove dead stems, prune hard in spring Note where cuts made…
Lavatera: early spring 10 minutes work! Look how much growth is removed!
Later…
Seven Sons Plant: Heptacodium miconioides
5 Brickell and Joyce DK Publishing, 2017 Brown and Kirkham ISBN 978-1465457608 Timber Press, 2004 ISBN 978-1-60469-002-6
6 Other references:
PNW-International Society of Arboriculture http://www.pnwisa.org/ Pruning information Publications Lists of Consulting Arborists
PlantAmnesty Sasquatch Books http://www.plantamnesty.org/ ISBN 978-1-57061-751-5 Pruning tips
Plant Amnesty
http://www.plantamnesty.org/ Mock Orange: Philadelphus lewisii
Russian Sage: Perovskia atriplicifolia Smooth Hydrangea: Hydrangea arborescens ‘Annabelle’
7 Snowball Bush: Viburnum opulus Wild Lilac: Ceanothus ‘Victoria’
Fuchsia Elderberry: Sambucus sp.
Mount Etna Broom: Genista aetnensis Jerusalem Sage: Phlomis fruticosa
8 Anemone Bush Bridal Wreath: Spiraea ‘Arguta’ Carpenteria californica
Privet: Ligustrum sp.
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