The Detroit Garden Center:  Feature Articles

Just one look at my summertime garden and you'll notice my unabated passion for Clematis (pronounced "klem`e-tus" or" "kli-mat`s"). In the last nine years, I've developed a small collection of at least 12 species and over 25 varieties. Nevertheless, I;ve barely scratched the surface of this vigorous garden delight.

The genus includes nearly 300 evergreen or deciduous species, including not only semi-woody to woody twining leaf climbers but so-called "herbaceous erect" perennials as well. Species hail from both hemispheres, including Europe, the Himalayas, China, Australasia, North America and Central America. The genus is characterized by leaf form, flower shape and great diversity in growth habits, from woody climbers reaching 30 to 50 feet to short-growing herbaceous perennials. Climbing species can easily clothe a wall, arbor or trellis, or small shrubs and trees by attaching themselves. Herbaceous forms make an attractive addition to your mixed or herbaceous border.

The most commonly available are generally grown for their beautiful flowers, followed by decorative seed heads. In fact, the value of Clematis as a cut flower is finally coming into its own, with growers such as Chalk Hill Clematis providing stock to the cut-flower trade, as well as offering plants to the nursery trade.

Flowers come in many shapes with four to ten petals including the star-shaped form with four petals (actually sepals); saucer shaped, single, large-flowered; double large-flowered; tulip-shaped; C. montana, looking like dogwood blooms; and C. viticellawith its upright flowers. The genus also has pendant forms, including open bell-shaped, bell-shaped, and tubular flowers. As an extra bonus, the flowers of some types, such as C. montana, are beautifully scented. Although the woody large-flowering hybrids are often available at your local garden center, species Clematis are now coming into their own in the green market.

The Species

Species Clematis are finally getting the recognition they have long deserved. As the varieties from which our large flowering hybrids are derived, they are worth knowing better.

C. florida. Of the florida species, 'Sieboldi' and 'Alba Plena,' are the most commonly available and are characterized by three- to four -inch exquisite flowers: first, white sepals with a mass of smaller, dark purple sepals in the center; the second, a mass of greenish white sepals resembling a pom-pom. Not vigorous growers and not recommended for the novice, they are best grown in a protected area to minimize excessive winter temperatures.

C. heraclifolia. Named for the resemblance of the species' leaves to those of cow parsley ( Heracleum spp.), C. heraclifoliais categorized as an "herbaceous erect" form. The plant dies back to the ground each year, developing over time, a woody crown from which new growth emerges late each spring. These one to three foot plants are ideal for the border, so keep them near the front of your beds. No one will believe these plants are Clematis, so they'll want to get a good look. The tubular flowers, resembling hyacinths in form, appear in small clumps and are usually blue, purple or white.

C. integrifolia. The other commonly available herbaceous erect species, C. integrifolia, also dies back to a woody crown, putting out new growth each spring. Each stem grows straight up for two to three feet, with pairs of alternating opposite leaves. The bud emerges from the last set of leaves, tips over and then opens inward to a flower consisting of four slightly twisted sepals. This unusual plant benefits from a little gentle support to keep its stems upright, although I like the rambling habit it develops as it flops into other plants.

C. macropetala. If you want early, profuse display in a Clematis, this is your plant. C. macropetalais the earliest blooming of Clematis generally available in our area, and it is stunning. This Clematis is characterized by a profusion of one- to one-and-a-half-inch pendant flowers consisting of longer outer sepals around a clump of shorter inner sepals. As with many Clematis, the seed heads are as intersting as the flowers on this variety, if left alone for the rest of the season.

C. montana. I almost lost first C. montan when I followed the directions on the tag and planted in full afternoon sun. Water it all I would, the poor thing shriveled up and almost died before I took note and moved it to a more suitable location. A note of caution: before you purchase any variety - species or hybrid - do your research to maximize your chances of success. C. montana varieties are characterized by pinkish to pinkish white flowers which closely resemble dogwood - four rounded petals set at 90 degrees. They can be quite vigorous in the right circumstances, growing sometimes to 30 feet. Relatively slow to establish, give them plenty of time, for you will be rewarded with a subtly beautiful display, including, in some forms, wonderful scents, including vanilla and lilac.

C. terniflora. Commonly known as the "Sweet Autumn Clematis," this species has had the most names in the briefest period of time; at least its most recent is relatively pronounceable! It is also one of the most vigorous - my original plant yearly threatens to pull down my porch, and throws off so much viable seed I have been able to cover much of my cyclone fence with delicious drifts of green and white in the early fall. The small star-shaped white flowers (four to five petals) cover the plant like a drift of snow, attracting beneficial insects with their delicious hawthorn-like scent. This plant will thrive even in a northern exposure - you really can't go wrong, as long as you prune it hard every year.

C. texensis. As my interest in Clematis species increased, I encountered C. texensis - notable for two reasons: it is native to North America (as its eponym indicates) and it is the only species having truly red flowers. In fact, if you come across a hybrid with red or near-red flowers, it is likely a C. texensisshows up somewhere in its development. The tubular flowers are one to two inches long, flaring out in a form resembling a small lilyflowered tulip. This species can be prone to powdery mildew, so be sure to site it where there is plenty of air circulation and away from your mildew-prone phlox and lilacs. These are woody twiners but Japanese hybridizers have been using them in the development of herbaceous erect cultivars destined for the ikebana flower trade.

C. viticella. Among my favorites of the woody climbers are the C. viticella varieties, especially 'Polish Spirit' with purple flowers, 'Madame Julia Correvon' with medium pink flowers and 'Alba Luxurians, true to its name, bearing a profusion of white flowers. C. viticellais a vigorous grower whose flowers, although not particularly large, are astoundingly numerous, sometimes covering the upper two-thirds of the plant with a riot of blossom. A mid-to-late bloomer, many representatives of this species flower well into the fall, the display dwindling from its greatest glory in late June to early July.

I recommend 'Polish Spirit' to gardeners looking for a hardy, consistent performer.

Just recently, varieties of C. alpina, C. durandii, C. orientalisand C. tanguticawere introduced to my garden. C. alpinavarieties are, like C. macropetala, characterized by pendent flowers. C. durandiiis a cross between C. integrifolia and C. jackmaniiand has smaller, blue flowers with five to six petals. Both C. orientalisand C. tanguticaare relatively unusual for their yellow-hued bellshaped flowers, again with four petals.

General Culture

Many - but not all - Clematis like full sun of at least six hours of direct sunlight, but there is a caveat here. As my Dad always said, Clematis "like cool feet." Site your Clematis where it will get at least six hours of direct sunlight during the growing season, but either shade the roots with another plant or mulch them heavily to prevent the soil from getting too warm. Some of mine are shaded with woody shrubs, others with herbaceous perennials. Most large-flowering hybrids abide by these rules, but be aware that some actually develop richer flower color if they are located in partial shade rather than hot afternoon sun. The key here is to know your species and varieties and to site your specimens accordingly. Clematis like well-drained, slightly alkaline soil, and the addition of organic matter is always welcome.

Sources

Barry Fretwell's A Comprehensive Guide to Clematis is a useful introductory source, focusing primarily on the more-commonlyseen large-flowering hybrids. This volume does not go into a great deal of detail regarding the overall genus, but does include excellent photographs of many of the large-flowering hybrids, especially useful when attempting to identify an improperly labeled purchase from your local nursery. Christopher Grey-Wilson's Clematis: The Genus is a much more technical source, describing all 297 known species in detail. Appropriately subtitled A Comprehensive Guide for Gardeners, Horticulturists and Botanists, Grey- Wilson also discusses cultivation, botany and issues of classification, making this an excellent resource for the serious enthusiast. Read more about Clematis as cut flowers in the May/June 2004 issue of Garden Design, available in the Detroit Garden Center Library. Horticulture's August 2004 issue has a wonderful article on the development of Japanese hybrids. Chalk Hill Clematis can be reached through their web-site at www.chalkhillclematis.com And, finally, Telly's in Troy has the best selection of Clematis I've come across so far, offering varieties of many of the species discussed here.