There are many dogwoods to choose from for your garden. They are an important food source for insects and birds, easy to grow in most conditions, and the flowers, foliage, and stems can add a delightful splash of colour to your garden space.

Reclassification of the Cornus genus

In 2011, the genus Cornus was divided into four phylogenetic and morphological distinct genera, yet the name changes have been slow to appear in the marketplace in gardeners’ circles and in online articles. For the purpose of this article, I will use the newer classification botanical names which are as follows, with examples of species commonly found in Ontario.

1. Cornus: woody species with precocious flowers: Cornus mas (non-native)
2. Benthamidia: woody species with large petaloid bracts: Benthamidia florida (native but rare in Ontario), B. kousa (non-native)
3. Swida: blue and white fruited (shrubby) dogwoods, woody without petaloid bracts:  Swida sericea, S. racemosa, s. alternifolia (all native)
4. Chamaepericlymenum: dwarf, herbaceous (groundcover) plants: Chamaepericlymenum canadensis (Bunchberry, native)

Benefits of adding dogwoods to your garden design

• Dogwoods are one of the top thirty keystone plants supporting caterpillars. Ninety-eight caterpillar species use dogwoods as their host plant.
• Four pollen specialist bee species collect pollen from dogwoods for their larvae.

Below, left to right, the Summer Azure butterfly (Celastrina neglecta) (a species whose caterpillars use dogwoods as hosts), and right, the pollen specialist Fragile mining bee (Adrena fragilis).  

Dogwoods are also larval hosts for, below left, the Polyphemus Moth and right, the Fragile White Carpet Moth.

Dogwoods are an important food source for birds, and mammals. Their berries and seeds are rich in protein, calcium and fat, supporting overwintering and migrating wildlife. Thirty-six species of birds feed on the drupes. The cedar waxwing is one of few North American birds  which specializes in eating fruit. 

Other reasons to consider adding dogwoods to your garden design:

• Most native dogwoods are fast growing, long-lived. and will grow in a variety of conditions from full sun to part shade and moist, well-drained soils. Large-flowered species prefer organically rich soils.
• They are easily propagated from cuttings and seeds, and for the suckering species, by division. The shrubby, suckering species are excellent in hedgerows and on slopes for erosion control.
• Many species have medicinal properties
• Most species are disease-resistant. (one Ontario exception: Benthamidia florida)
• Flowering dogwoods, especially B. florida , are ‘calcium pumps’; their calcium-rich leaves decompose quickly (faster than most other tree species), increasing the availability of calcium and other nutrients on the forest floor. 
• Dogwoods add stunning colour to the garden, from the beautiful flowers of the large-bracted trees in spring, to the bright red, yellow and orange stems of woody suckering shrubs in fall and winter. 

Four flowering dogwoods for spring colour

First, in late March or early April, my Cornelian cherries start to bloom. Their clusters of small yellow flowers along the branches not only herald in the end of winter, but provide nourishment for early-emerging bees and other insects. In late summer/fall, their bright red astringent fruit light up the small trees. Native to southern Europe and southwest Asia, they have an ancient medicinal history; their edible fruit, for example, possesses anticoagulant, antioxidant and anti-inflammatory properties. Cornelian cherries form large, multi-branched shrubs which can be trained into small trees. While monoecious, they produce more fruit with more than one plant. Plants often take several years to fruit, as young plants produce male flowers only. While known to sucker, my Cornelian cherries have yet to do so after 8 years in the garden. Height: 5-7m

Below, from left to right, Cornus mas (Cornelian cherry, and the cultivar C. mas ‘Aurea Eglantissima’).

Second, blooming weeks after the Cornelian cherry, the native eastern flowering dogwood  (Benthamidia florida) displays large, usually white to pink flowers. The true flowers, however, are the small, yellowish-green florets in the centre surrounded by the four colourful, petal-like, bracts (modified leaves). This beautiful landscape tree is native to north eastern North America and is considered a species at risk in Ontario, native only in the extreme south of the province. This species is threatened by dogwood anthracnose which attacks the leaves and spreads throughout the branches and trunk; fortunately, there are now resistant varieties available on the market. The fruit are an important food source for birds and other wildlife, but are considered inedible for humans. Height: 4-9m 

Above, left, the white Benthamidia florida photographed at the New York Botanical Gardens by Ryan Somma, Creative Commons; right, B. florida rubra, https://plants.ces.ncsu.edu 

Third, blooming several weeks after the eastern flowering dogwood, is the Asian kousa dogwood (Benthamidia kousa), available in over 100 varieties. This is a small tree or multi-stemmed shrub that is anthracnose-resistant, drought resistant, and hardier than B. florida.  Like the blossoms of the eastern flowering dogwood, the kousa dogwood has long lasting, showy, petal-like bracts which are more pointed. The attractive, strawberry-like fruit is high in fiber, vitamins and minerals and  is eaten by wildlife and humans alike. A common tree in permaculture gardens, the fruit is reportedly high in anti-oxidants, and possesses anti-inflammatory and anti-cancer properties. Height: 4-9 m

Below, left and centre, B. kousa ‘Wolf Eyes’, and right, B. kousa ‘Stellar Pink’.

Last to bloom in late spring in my garden is the pagoda dogwood (Swida alternifolia). Native to Ontario, this small tree or multi-stemmed shrub is famous for its lovely horizontally-layered branches, late spring flowers, and midsummer blue berries which, in my garden, are quickly gobbled up by robins. S. alternifolia ‘Golden Shadows’ is a smaller variety with leaves that are bright yellow with a band of green in the centre.  Both prefer part sun with afternoon shade.   Height: 4-8m

Colourful shrubby dogwoods that shine even in the winter garden

Our native red osier dogwood (S. sericea) and the two cultivars shown below, ‘Bayleyi’ and ‘Flaviramea’, are visually stunning in the winter garden. ‘Bayleyi’ has bright red winter stems, and does not sucker like its parent. Red osier dogwood has white drupes, prefers average to moist soil, and grows in full sun to shade. Height: 2-3m

C. sanguinea (Blood-twig dogwood), native to Europe and western Asia, also has several colourful cultivars for the winter garden. Below, left, S. sanguinea, and, right, S. sanguinea ‘Midwinter Fire’.   Height: 3-6 m

A native for wildlife

Our tall, native, gray dogwood (S. racemosa) suckers profusely, and is thus well suited for a hedgerow and/or for erosion control along riverbanks and ravines. It offers safe nesting sites for birds, nectar for late spring insects like bees and butterflies, and a bounty of white fruit in the fall for migrating birds and other wildlife.   Height: 4-5 m

Pruning shrubby dogwoods to maintain plant colour

 Shrubby dogwoods benefit from pruning to maintain the vivid colour of their stems. The following, from Horticulture magazine, explains how to prune your shrubby dogwood. 

• It is recommended to prune once a season after the shrub has been in the ground for a year or two, removing 1/3 of the oldest stems.
• The best time to prune is in February, when the plant is dormant. The cuttings can be rooted for planting out the following fall.
• Cut stems that are dead, diseased, or growing at a  bad angle to the ground. For those that are old (colour is greyish or dark greenish), cut back to a pair of buds between ground level and a height of around 40 cm.
• You can also hard-prune an overgrown shrubby dogwood to rejuvenate it. Cut all stems back to about 10 cm above the ground above the first or second leaf node.

Bunchberry (Chamaepericlymenum canadensis)

In 2017, to celebrate Canada’s 150th anniversary, Master Gardeners of Ontario sponsored a nation-wide contest to pick Canada’s national flower, and the winner was the bunchberry! Bunchberry is a lovely stoloniferous ground cover, requiring acidic, moist, well-drained soil. Like  the flowering dogwood, it has a white flower with showy bracts that appear in early summer. Its red berries are consumed by wildlife and, unlike those of B. florida, by humans. Plant in a site sheltered from afternoon sun and winds.

Resources

• Cornaceae: Dichotomous Key: Go Botany 
• When Botanical Names Change: Understanding Plant Reclassification — Chris Welch’s Horticulture Field Guide 
• Keystone Native Plants – Eastern Temperate Forests – Ecoregion 8
• Flowering dogwood (Cornus florida L.) as mediator of calcium cycling: new insights are revealed by analysis of foliar partitioning | Trees
• Land Snails Ecology – Forest Calcium
• Cornus mas and Cornus Officinalis—Analogies and Differences of Two Medicinal Plants Traditionally Used – PMC
• Kousa Dogwood Fruit: Description, Flavor, Benefits, And Uses – Gardeners’ Magazine
• Pruning Dogwood Can Help Maximise The Ornamental Appeal Of Their Colourful Stems | Horticulture Magazine