Here are two articles published in the Calgary Hort Society newsletter. I hope listing the info here is alright as I've listed the writers. Both articles indicate that the climate is NOT suitable for group B clematis and will only put on a disappointing display of bloom. However, their are still lots to choose from. Here's a website with some good information on clematis
Care must be taken to choose only those varieties suitable for Calgary’s climate. The clematis species and varieties that grow well here can be divided into three distinct groups, based on their pruning requirements. The first group, Group A, comprises small-flowered species and hybrids that bloom in spring on old wood produced the previous year. These are best left unpruned except for tidying them up to prevent woody overgrowth. Of this group only Clematis alpina and C. macropetala and their cultivars do well in our climate. Other early-blooming species and hybrids, such as C. montana, are a disappointment as they usually winter-kill to the ground.
Clematis alpina and C. macropetala and their many cultivars are perfectly hardy here and very seldom die back. They have dainty, fern-like foliage and elegant, drooping flowers in lavish profusion, followed by ornamental silky plumes of seed. The main flush of flowering occurs in May, after which wayward growth may be pruned back lightly. New growth will quickly flourish and may even provide a late-summer show of repeat bloom.
Clematis alpina has satiny, blue, nodding flowers, usually with four long pointed sepals and a tuft of paler staminoids in the center. Recommended cultivars: ‘Frances Rivis’ blue, lantern-like flowers ‘Frankie’ bright mid-blue flowers ‘Pamela Jackman’ full, purple flowers ‘Ruby’ red nodding flowers ‘Willy’ pale pink flowers
Clematis macropetala is a similar species but the pendant, mauve/cream flowers appear to be double as the centre tuft of staminoids is well developed. Recommended cultivars:
‘Blue Bird’ dark blue bells, vigorous ‘Maidwell Hall’ deep blue flowers ‘Rosy O’Grady’ ballet skirts of rich rose ‘White Swan’ large white double flowers.
Group B includes all of the large-flowered hybrids, single or double, that bloom in early summer on the previous year’s growth (old wood), and in late summer on new wood. In gentler climes, the flowering season starts in mid-June with a large burst of colour, with some cultivars blooming right through to the first frost. Since many of these plants are of borderline hardiness, as far as the old wood is concerned, we seldom get the early summer show and must settle for a few miserable blooms much later in the season. Cultivars which MAY NOT flower well on their summer growth are listed below:
‘Barbara Dibley’ petunia red, ‘Dr. Ruppel’ carmine with pale edges ‘Duchess of Edinburgh’ large double white ‘Miss Bateman’ white with dark stamens ‘Nelly Moser’ rosy-mauve/carmine bar ‘Ramona’ rich lavender, wavy sepals ‘Vyvyan Pennell’ double lavender blue
Other Group B cultivars, sometimes referred to as Group B/C, reliably produce a good crop of flowers on the current season’s growth in July and August. These are better selections for our climate:
‘Henryi’ white with brown stamens; ‘Madame le Coultre’ also called ‘Marie Boisselot’ huge, flat, pure white ‘Mrs. Cholmondeley’-lavender/mauve ‘Niobe’ deep ruby red ‘The President’ deep purple blue ‘Violet Charm’ deep violet, floriferous ‘William Kennett" deep lavender blue ‘Elsa Spath’ deep violet blue.
Group B clematis require light pruning to tidy them up each spring, cutting back all dead wood down to existing healthy buds.
Group C is the best group of vining clematis for our climate as ALL of the flowers are produced on the current season’s growth (new wood); they are pruned back close to the ground in the fall or early spring. Flowers are produced in great quantity from mid-July through August, some cultivars blooming until frost. This section includes some of the most popular and famous of all large-flowered clematis hybrids and some very interesting late-blooming species. Recommended large-flowered cultivars:
‘Comtesse de Bouchaud’ satiny, mauve-pink ‘Ernest Markham' petunia red (magenta) ‘Etoile Violette’ deep purple, hardy ‘Gipsy Queen’ velvety violet purple ‘Hagley Hybrid’ also called ‘Pink Chiffon’ pale pink, low-growing ‘Huldine’ pearly white, mauve bars on reverse x jackmanii rich purple flowers ‘Mme Edouard Andre’ wine red, pointed sepals, low grower ‘Margaret Hunt’ dusky mauve pink ‘Pink Fantasy’ pale pink/darker bar ‘Perle d’Azur’ pale, pure blue stars ‘Rouge Cardinal’ glowing crimson red ‘Star of India’ deep purple-blue/red bar ‘Victoria’ soft heliotrope mauve ‘Ville de Lyon’ carmine red, very choice
Other clematis in Group C bear smaller but striking flowers produced in such profusion that they make a fine show. No garden should be without these lovely plants which are hardy, even on exposed fences. Recommended choice species and their cultivars:
Clematis texensis tulip-shaped, fuchsia-pink ‘Duchess of Albany' pink upright bells ‘Gravetye Beauty’ scarlet-red, tulip-like ‘Pagoda’ pink-mauve, nodding
Clematis viticella small, purple, nodding ‘Abundance’ wine-rose bell-like flowers ‘Alba Luxurians’ white bells with green tips ‘Kermesina’ (rubra) deep crimson, flaring ‘Little Nell’ cream-white/mauve edges ‘Margot Koster’ rose pink bellflowers ‘Minuet’ white/mauve, nodding ‘Purpurea Plena’ also called ‘Mary Rose’ mauve, double, open ‘Purpurea Plena Elegans’ double violet purple nodding ‘Royal Velours’ deep velvet purple bells ‘Venosa Violacea’ purple stars/white centres.
In addition to these are robust rambling species with delicate foliage and tiny flowers produced in great profusion:
C. x jouiniana ‘Praecox’ pale mauve, late C. ligusticifolia fluffy white panicles ‘Prairie Traveller’s Joy’ a choice selection C. orientalis yellow pendant flowers C. serratifolia ‘Grace’ creamy white bells C. tangutica bright yellow lanterns
The latter four require hard spring pruning to keep them in bounds as the old wood overwinters but flowers are only produced on new wood; they become overgrown and tangled if neglected.
Another group of clematis behave more like hardy herbaceous perennials. Although not tall, they require some staking or planting near a bush for support. Treat these as border plants:
C. heracleifolia davidiana tiny, fragrant, mauve C. integrifolia small, nodding, indigo C. x durandii rich blue, yellow stamens C. recta many small creamy flowers
When shopping for clematis make your list from these recommended varieties; they are known to do well here.
- Ken Girard and Judith Doyle
Once again confusion and ignorance raise their ugly heads when it comes to the best clematis to grow here in Calgary. The fact is, NOT ALL CLEMATIS ARE HARDY OR RELIABLE HERE! I will, again, do a quick run-through of the ones to grow and the ones to avoid. This information comes from over 100 years of cumulative gardening experience in Calgary - not Victoria, or some book written in a milder climate. Newcomers take warning: some of your old favourites are definitely not hardy here. To be safe, choose from the following two groups: Group A or Group C. Group A - Of the spring-flowering clematis that bloom on old wood (last year’s growth) in the spring (no pruning needed), two species and their cultivars are garden worthy and hardy: Clematis alpina and C. macropetala. They can be grown anywhere you want - on the house, garage, or shed, up shrubs and trees, on the back fence, or even in the back forty! Other species in this section worth looking for and trying: Clematis occidentalis, C. columbiana and C. koreana. Others, such as C. montana, often offered here, SHOULD BE AVOIDED unless you want to do a lot of work protecting their wood through winter. Do not be tempted! Group C - Summer-flowering clematis bloom on each year’s new growth, a very important feature, as the wood of most modern clematis is NOT HARDY HERE!!! We need to plant varieties that flower on the current season’s growth. (Prune last year’s wood to the ground in late fall or early spring.) In Group C are the ever-popular large-flowering hybrids such as C. x jackmanii, ‘Ville de Lyon’, ‘Ernest Markam’, ‘Margaret Hunt’, ‘Hagley Hybrid’, ‘Comtesse de Bouchaud’*, and ‘John Huxtable’, to name just a few. Large-flowered hybrids do best planted against walls, which afford extra protection from wind and extreme cold. There are also small-flowered hardy species and hybrids that bloom on new growth in summer. These include Clematis viticella and all its hybrids and selections. Vigorous growers and prolific bloomers these will grow almost anywhere in the garden. Some are more vigorous than others but most do well.
ONES TO AVOID Do not be tempted!! Group B - These large-, sometimes huge-, flowered hybrids bloom best on old wood (last year’s growth) in May. This wood is seldom hardy in our climate so this means: NO flowers! True, some plants in this group - the B-2s - bloom again later in summer on their new growth; the down side is that they do not flower as heavily in this second flush. On plants that usually have double flowers in spring, the only flowers you will see are single, as only flowers produced in spring on old wood are double and prolific. Like Katrina at Vale’s Greenhouses, who wants to stamp out dracaenas, I want to stamp out ‘Nelly Moser’ (the clematis that is). My parents live in Hope (Zone 6) and grow ‘Nelly Moser’ which bears hundreds of flowers every May; the best I have seen it do here is six pathetic faded flowers. I ask you, why bother? If you are purchasing your first clematis, or plan on having only one or two in your garden, I don’t care how tempting ‘Blue Ravine’, ‘Duchess of Edinburgh’ or ‘Vyvyan Pennell’ are, don’t waste your money! Plant the right clematis for our climate and you will be rewarded with lots of flowers and a plant you can enjoy for many years to come. Plant the others, and “Caveat emptor!” *Yes, Bouchaud, not Bouchaurd.
C. alpina & cultivars C. macropetala & cultivars: Bluebird, Burford White, Columbine, Constance, Flamingo, Frances Rivis, Frankie, Helsingborg, Jacqueline du Pre, Jan Lindmark, Lagoon, Maidwell Hall, Markam’s Pink, Pamela Jackman, Rosy O’Grady, Ruby, White Moth, White Swan, Willy, C. columbiana, C. koreana, C. occidentalis
(large-flowered hybrids) Allanah, Anna, Ascotiensis, Blue Angel (Blekitny Aniol), Comtesse de Bouchaud, Dorothy Walton, Edward Prichard, Ernest Markham, Gypsy Queen, Hagley Hybrid (Pink Chiffon), Jackmanii, Jackmanii Superba, John Huxtable, Kacper (Kasper), Kalina, Kardinal Wyzynski, King George V, Lady Betty Balfour, Lilacina Floribunda, Lucey, Margaret Hunt, Mme Baron Veillard, Mme Eduard Andre, Monte Cassino, Perle D’Azur, Perrin’s Pride, Pink Fantasy, Prince Charles, Rouge Cardinal, Serenata, Silver Moon, Sir Trevor Lawrence, Star of India, Sunset, Twilight, Victoria, Ville de Lyon, Voluceau
(small-flowered hybrids) Abundance, Alba Luxurians, Betty Corning, Blue Belle, Blue Boy, Carmencita, Duchess of Albany, Durandii, Emily Plater, Elvan, Etoile Violette, Gravetye Beauty, Huldine, Kermesina (Rubra), Little Nell, Margot Koster, Mary Rose, Minuet, Mme Julie Correvon, Pagoda, Polish Spirit, Purpurea Plena Elegans, Royal Velours, Tango, Venosa Violacea.
- Ken Girard
Hope this helps! You may even want to consider joining the Calgary Horticultural Society :)