Shrubs are woody perennials that produce multiple stems, shoots and branches from the base of the plant. Generally, they survive winter without dying back to the ground as herbaceous perennials do. There is no clear distinction between a shrub and a tree: a shrub is usually lower growing and multi-stemmed, but it can also be single stemmed, like a tree.
Uses
Shrubs have no defined maximum height, and can range in size from a creeping groundcover to a small tree. This variety in size and their versatility make shrubs an important feature of the garden. They can be used as structural plants to divide a large garden into smaller, more functional spaces or to frame an attractive viewpoint or disguise a less desirable feature. Used along a garden boundary, they provide shelter and privacy and block the noise of traffic. They are an important component of foundation plantings or in mixed borders with perennials. And in any size garden, a shrub with an elegant shape can be a focal point, perhaps as a feature in a new front garden, underplanted with spring ephemerals and hardy native groundcovers.
In addition to their growth habit (height, width, form), shrubs are chosen for other desirable characteristics, such as:
- Foliage (colour, form, texture)
- Flowers (colour,fragrance)
- Fall interest with fruit, berries or colourful foliage.
- Winter interest through bark, structure or form
- A food source, habitat, nesting material to attract wildlife, birds and insects
As important as shrubs are to us as garden plants, they are also a critical third layer for local wildlife, occupying the space between the tall tree canopy and ground-hugging perennials. Native shrubs play a significant role in the work of nature, providing a variety of pollen, nectar, seeds, fruits and nesting sites along with needed protection from predators. For more on the benefits of gardening with native shrubs, see Gardening with Native shrubs: A Toronto Master GardenersGuide.https://www.torontomastergardeners.ca/gardeningguides/gardening-with-native-shrubs-a-toronto-master-gardeners-guide/
Considerations when choosing a shrub
Choose plants suited to the growing conditions of your site rather than attempting to change the site to suit the plant. Plants growing in their preferred locations are likely to be healthier than plants growing in less-than-optimal conditions and are therefore more able to withstand disease and pest problems than plants that are under stress. Make sure your plants are at least hardy for your gardening zone. Native plants can be an ideal choice if they are given the correct growing conditions.
Light: One of the most important factors in choosing plants will be determining the amount of available sun/shade. While most shrubs are fairly adaptable in their light requirements, some may produce fewer flowers in a shady location.
Light conditions can be classified as follows:
- Full sun – plants require at least 6 hours of direct, late-morning/afternoon sun
- Partial shade – plants need 4 to 6 hours of morning or afternoon sun, but should be shaded from the hot, midday sun.
- Full Shade – plants can tolerate less than 4 hours of sun, preferably in the morning. A bright location that receives no direct sun would be classified as full shade.
Soil texture and moisture: Other factors to consider when choosing shrubs are soil texture (primarily clay, sand, loam or silt) and soil pH (acid or alkaline). The moisture of your garden soil will also be a consideration: some shrubs will thrive in dry conditions and others will like consistent moisture. Sandy soils will drain quickly while clay soils hold onto water in the root zone and may become waterlogged. For more information on soil, see Soil Fertility: A Toronto Master Gardeners Guide.https://www.torontomastergardeners.ca/gardeningguides/soil-fertility-a-toronto-master-gardeners-guide/
Size of plant: Another important, but often missed consideration, is the shrub’s size at maturity. Checking mature height and width will tell you the amount of space the shrub will need for optimum growth, so be aware of possible restrictions from surrounding structures and plants.
A small plant can be a good choice. Not only will it be cheaper, but smaller shrubs are easier to plant and will adapt more quickly to their new location, making up the size difference relatively quickly. For more tips on successful planting, see Planting a Tree for Life: A Toronto Master Gardeners Guide. https://www.torontomastergardeners.ca/gardeningguides/planting-a-tree-for-life-a-toronto-master-gardeners-guide/
Maintenance
Once established, shrubs require very little maintenance. They need to be watered regularly when first planted and may need supplemental water in times of drought. A top dressing of leaf litter or compost, laid on the soil around the plant as mulch, will protect the soil from erosion and compaction while helping to retain moisture. As the mulch decomposes, nutrients are returned to the soil to promote healthy plant growth. Wood chips can also be a good garden mulch for plantings with shrubs and trees.
Pruning
Shrubs are pruned for many reasons, including shaping, reducing size, removal of broken and diseased branches, thinning, rejuvenation and increasing flower and fruit production.
The most common mistake made when pruning flowering shrubs is pruning at the wrong time. In general, flowering shrubs fall into two groups:
- The first group are the early spring flowering shrubs, such as forsythia and lilac. They bloom on “old” wood produced the previous season and if pruning is needed, it should be done immediately after flowering.
- The second group are the later flowering shrubs, such as hydrangea, that bloom on “new” wood, this year’s growth. They should be pruned in early spring, before new growth begins.
Deadheading (the removal of spent flowers) is a form of pruning. Some shrubs, such as lilacs, may benefit from deadheading as this process will help the plant put more of its energy into growth, rather than seed formation.
Avoid pruning in late fall as you do not want to stimulate new growth late in the season. You will want to allow time for any previous pruning cuts to heal over, helping to prevent winter dieback. Spring pruning can be performed as soon as the temperatures rise around the freezing mark and are guaranteed not to plunge dramatically.
Good garden practice for healthy plants
In general, shrubs are easy to grow if given the right conditions. However, common pests, such as aphids, leafminers, caterpillars, beetles, borers or scale may attack. Some members of the viburnum family are often targeted by the viburnum leaf beetle. Be aware also of fungal diseases, such as verticillium wilt, anthracnose, cankers and powdery mildew.
Here are some strategies for maintaining the health of your plants:
- Remove any weeds as they appear and before they set seed
- Prune out diseased branches promptly, using sterilized tools
- Remove diseased plant material off-site; do not place in garden compost
- Water new plants well through the first growing season, continuing into fall
- Avoid pesticides which can move up through the food chain. Use organic methods, such as soap spray or horticultural oil, and only as a last resort. Remember that there may already be many beneficial organisms such as birds and frogs, or predatory insects, such as parasitic wasps, sawflies, beetles and spiders in your garden, looking for a handy meal. By not using pesticides, you are helping nature keep pests under control and sustaining a healthy environment.
- Amend your soil with organic matter such as compost, leaf mould or healthy plant debris laid on the soil surface, not dug in. This is preferable to using fertilizers, such as bone meal, which may disrupt the mycorrhizal fungi in the soil.
- A mulch of leaf litter or wood chips will protect the soil from erosion and compaction while helping to retain moisture. As the mulch decomposes, it returns valuable nutrients to the soil.
- Take care of your garden soil by digging as little as possible and never when the soil is wet. Avoid walking on your garden beds which also compacts the soil.
Recommended species/varieties/cultivars; Plants native to Ontario marked with N
Shrubs for full sun
- Bottlebrush buckeye (Aesculus parviflora)
- Carolina allspice (Calycanthus floridus)
- Peashrub (Caragana arborescens)
- Bluebeard (Caryopteris x clandonensis) and cultivars
- Buttonbush (Cephalanthus occidentalis) N
- Japanese flowering quince (Chaenomeles japonica) and cultivars
- Smokebush (Cotinus coggygria) and cultivars
- Cotoneaster (Cotoneaster spp.)
- Deutzia (Deutzia gracilis) and cultivars
- ‘Northern Gold’ forsythia (Forsythia ‘Northern Gold’) and other cultivars
- ‘Arnold Promise’ witch hazel (Hamamelis x intermedia ‘Arnold Promise’)
- Rose of Sharon (Hibiscus syriacus) and cultivars
- Cinquefoil/Potentilla (Potentilla fruticosa) and cultivars
- Purple-leaf sand cherry (Prunus x cistena)
- Purple willow (Salix purpurea ‘Gracilis’/’Nana’) and other species
- Common elderberry (Sambucus canadensis) N
- Black Beauty elderberry (Sambucus nigra f. porphyrophylla ‘Gerda’) and other cultivars
- Spirea (Spiraea x bumalda, S. japonica, S. nipponica) and other cultivars
- Preston lilacs (Syringa x prestoniae) and cultivars
- Dwarf Korean lilac (Syringa meyeri ‘Palibin’)
- ‘Miss Kim’ lilac (Syringa pubescens subsp. patula ‘Miss Kim’)
- Bloomerang purple lilac (Syringa ‘Penda’) and other Bloomerang cultivars
- Koreanspice viburnum (Viburnum carlesii)
- ‘Summer Snowflake’ viburnum (Viburnum plicatum f. tomentosum ‘Summer Snowflake’)
- Highbush cranberry (Viburnum trilobum) N
- Weigela (Weigela florida) and cultivars
Shrubs for sun/part shade
- Cutleaf Japanese maple (Acer palmatum Dissectum Viride Group) and other cultivars
- Serviceberry (Amelanchier spp.) N
- Black chokeberry (Aronia melanocarpa) N
- Summersweet (Clethra alnifolia) and cultivars
- Ivory Halo dogwood (Cornus alba ‘Bailhalo’)
- Alternate-leaf dogwood (Cornus alternifolia) N
- Cornelian cherry (Cornus mas)
- Red osier dogwood (Cornus sericea) N
- ‘Carol Mackie’ daphne (Daphne x burkwoodii ‘Carol Mackie’)
- Bush honeysuckle (Diervilla lonicera) N
- Redvein enkianthus (Enkianthus campanulatus)
- Dwarf fothergilla (Fothergilla gardenii) and cultivars
- Panicle hydrangea (Hydrangea paniculata) and cultivars
- St. John’s wort (Hypericum kalmianum) N
- Winterberry (Ilex verticillata) N
- Little Henry sweetspire (Itea virginica ‘Sprich’)
- Star magnolia (Magnolia stellata) and cultivars, such as Little Girl series
- Bayberry (Morella pensylvanica) N
- Tree peony (Paeonia x suffruticosa) and cultivars
- Golden mock orange (Philadelphus coronarius ‘Aureus’) and other cultivars
- Ninebark (Physocarpus opulifolius) N and cultivars
- Chokecherry (Prunus virginiana) N
- Fragrant sumac (Rhus aromatica) N
- ‘PJM’ rhododendron (Rhododendron PJM Group) and other cultivars
- ‘Northern Hi-Lights’ azalea (Rhododendron ‘Northern Hi-lights’) and other cultivars in the Northern Lights series
- Flowering raspberry (Rubus odoratus) N
- Arrowwood viburnum (Viburnum dentatum) N
- Wayfaring tree (Viburnum lantana
Shrubs for sun to full shade
- Bottlebrush buckeye (Aesculus parviflora)
- Silverleaf dogwood (Cornus alba ‘Elegantissima’) and other cultivars
- Gray dogwood (Cornus racemosa) N
- Common witch hazel (Hamamelis virginiana) N
- ‘Annabelle’ hydrangea (Hydrangea arborescens ‘Annabelle’)
- Oak-leaved hydrangea (Hydrangea quercifolia) and cultivars
- Japanese kerria (Kerria japonica) and cultivars
- Oregon grape (Mahonia aquifolium)
- Northern spicebush (Lindera bezoin) N
- Cutleaf staghorn sumac (Rhus typhina ‘Dissecta’)
- Alpine currant (Ribes alpinum)
- Wild black currant (Ribes americanum) N
- Snowberry (Symphoricarpos albus) N
- Nannyberry (Viburnum lentago) N
Invasive species
Many lists of ornamental shrubs will include shrubs such as barberry (Berberis thunbergii), burning bush/winged euonymus (Euonymus alatus), privet (Ligustrum amurense) and non-native honeysuckles (Lonicera spp.). These invasive plants can spread into natural areas and have an adverse effect on local native plants. For this reason, they are not recommended. For information about invasive plants and non-invasive alternatives, see the link below to the Grow Me Instead brochure.
Resources and References
Grow Me Instead: beautiful non-invasive plants for your garden. Ontario Invasive Plants Council, 2020. https://www.ontarioinvasiveplants.ca/wp-content/uploads/2020/04/Southern-Grow-Me-Instead-1.pdf
Beck, Alison and Kathy Renwald. Tree and shrub gardening for Ontario. Lone Pine Publishing, Edmonton, AB, 2001.
Bennett, Jennifer. Dryland gardening: plants that survive and thrive in tough conditions. Firefly Books, Richmond Hill, ON, 2005.
Cole, Trevor. Gardening with trees and shrubs in Ontario, Quebec and the northeastern U.S. Whitecap books, Toronto, ON,1996.
Date published: May 2022
Prepared by the Toronto Master Gardeners, these Gardening Guides provide introductory information on a variety of gardening topics. Toronto Master Gardeners are part of a large, international volunteer community committed to providing the public with horticultural information, education and inspiration. Our goal is to help Toronto residents use safe, effective, proven and sustainable horticultural practices to create gardens, landscapes and communities that are both vibrant and healthy.
Statement on Invasive Plants: When choosing plants, avoid invasive plants, which can spread quickly and dominate gardens. Invasive plants are sold by nurseries, big box stores or even at community plant sales. Invasives may already be present in your garden. They can invade gardens by spreading from under a neighbour’s fence or may be transported by wildlife. For beautiful, sustainable options to invasive plants, see the Ontario Invasive Plant Council’s “Grow Me Instead – Beautiful Non-Invasive Plants for your Garden” at https://www.ontarioinvasiveplants.ca/resources/grow-me-instead/ before purchasing or accepting “gifts” of plants.
Statement on Home Remedies: The Toronto Master Gardeners do not recommend home remedies, as these have not been proven effective through scientific investigation, and may even damage other living organisms in the soil or plants in your garden. There are other garden friendly options you can use.
If you have further gardening questions, reach us at our gardening advice line 416 397 1345 or by posting your question here in the Ask a Master Gardener section. To book Toronto Master Gardener volunteers for talks, demonstrations, advice clinics, or other services, please contact us at 416 397 1345 or bookamg@torontomastergardeners.ca