Ilene Sternberg is an award-winning freelance garden writer and co-author of Best Garden Plants for Pennsylvania and Perennials for Pennsylvania

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Clematis 101
by Ilene Sternberg       #Flowers   #Plant Profile   #Vines

Clematis ‘Étoile Violette’

Virtually all clematis books are British. I think it’s some kind of law. According to those books, you may pronounce it “klem-a-tiss,” “kli-mah-tiss,” “klem-at-iss” or “klem-ay-tiss.” The plants are fabulous, and will respond no matter how you address them. Most Americans only spiral one up their mailbox post, but the Brits have been exploring the potential of almost 300 species and even more varieties and cultivars, using them far more imaginatively in their gardens for eons.

Clematis can reach 30 feet or be shorter than 2 feet. Flowers can be 10 inches across, or tiny stars, flat, cupped, turk’s cap-, bell-, urn- or tubular-shaped; sometimes delightfully scented, with fluffy, silky seedheads; and boast a broad spectrum of colors. In addition to greeting you while you peruse your junk mail, they can grace a container, clamber up a fence, ramble over rocks, climb trees, lace through shrubs and scamper across the ground. These buttercup relatives can also be alpine plants or little shrubs, not vines at all.

Susan Austin of Completely Clematis Specialty Nursery in Ipswich, Mass. (, has some pretty avant garde ideas about how to grow clematis. She uses cinnamon as a bactericide and fungicide. To battle periods of drought that can stunt growth and flower size, she recommends (in addition to deep planting, thorough watering once a week and heavy mulching) stuffing pre-moistened hydrogel (Soil-Moist or Terrasorb) into 6-inch-deep holes dug every 12 inches around each plant. Her trick is to soak the polymer beads in warm water prior to use. She says effects last as long as three years, by which time plants should be well established.

Avant-garde (C. ‘Evip033’)

Clematis have been customarily classified according to their pruning requirements. In Trouble-Free Clematis: The Viticellas (Garden Art Press, 1998), John Howells regroups them into 12 categories in order of their progression of bloom, dwelling more on the characteristics of the types and claiming the newer format is more useful and easily understood. Frankly, while I find attempts to systematize this mind-boggling array truly admirable, I am equally confused by both methods of organization. But, what do I know? I can’t sort socks, let alone clematis.

Clematis ‘Piilu’

Culture is more or less similar for all 12 groups. Like poppies, they should have their crowns sunk several inches below soil level when planted. Clematis fare best in good, neutral soil. Dan Long of Brushwood Nursery ( in Athens, Ga., says, “Amend soil with organic matter and consider some bonemeal, too. Plant clematis at a 45-degree angle – actually lean it over in the hole – to promote more shoots from the base sooner.”

“Never tease the roots of C. orientalis, C. alpina, C. macropetala or other fibrous-rooted types when planting,” Austin cautions. Taunting those temperamental roots can trigger sudden death. This sensitivity also makes transplanting difficult.

Most clematis can be pruned in early spring or late winter down to the first pair of buds, but leave pruning of early blooming kinds for after flowering or you’ll lose the spring show. Unless they’re tangled, you may leave them alone altogether. Broken stems, though, can invite a fungus, Phoma clematidina, that causes a stem rot and leaf spot disease where stems unexpectedly collapse in a melodramatic faint, which mainly affects large-flowered clematis hybrids. Species clematis, their cultivars and small-flowered hybrids are much less susceptible. Cut affected stems to ground level and the plant often recovers, usually the same season. Don’t be so quick to remove “dead” clematis. Sometimes dead-looking stems have perfectly fine growth at the top, and plants often resurrect magically after having been gone for years. Clematis sometimes lose their lower leaves as the season progresses. Underplanting with shallow-rooted, noninvasive plants can provide cover for this shameless nudity.

Clematis viticellas and its cultivars are easy to grow. I can’t say enough good things about the Pennsylvania Horticultural Society Gold Medal winner ‘Betty Corning’. Little lavender-blue fairy hats abound continuously from early spring until frost. Her leaves are pristine and never turn black. Stems are plentiful and sturdy. ‘Etoile Violette’ is no prima donna either; she is vigorous, floriferous and nearly indestructible. Dan Long, smitten with yellow C. tangutica ‘Lambton Park’, says, “Small-flowered clematis combined with disease-resistant roses are hot these days. People want performance in the garden without trouble or chemicals to get there.”

‘Prince Charles’ and ‘Margaret Hunt’ are two of Susan Austin’s recommendations for prodigious bloom. Beautiful Baltic cultivars are now the rage in Britain. Susan also is smitten with C. integrifolia ‘Aljonushka’, with strawberry colored blossoms.




Top Left: Clematis ‘Duchess of Edinburgh’

Bottom Left: Josephine (C. ‘Evijohill’)

Right: Clematis ‘Rooguchi’

While most clematis prefer having their heads in sun, Blue Moon (C. ‘Evirin’) and ‘Silver Moon’ show their true colors (pale lavender, almost gray) in shady settings. My latest crush is the enticing C. integrifolia x ‘Rooguchi’, bearing nonstop 2½-inch deep-purple open-bell-shaped flowers with recurved sepals, and a loose, sprawling habit. It blooms even in shade from May through September.

Three reliable, virtually infallible large-flowering types are white ‘Henryi’, purple ‘The President’ and blue ‘Ramona’.

I’m working my way through Christopher Grey-Wilson’s book Clematis: The Genus (Timber Press, 2000). According to that, I still have 661 other clematis I haven’t tried.

Clematis terniflora


A version of this article appeared in a March/April 2014 print edition of State-by-State Gardening.
Photography courtesy of Ilene Sternberg.


Posted: 04/10/17   RSS | Print


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