Issue 10, 1997 Plant Evaluation Notes Clematis for Northern Landscapes Richard G. Hawke, Coordinator of Plant Evaluation Programs ou have decided to plant a clematis in exist, including virgin’s bower, old man’s beard, Clematis alpina and C. macropetala are true your garden, but which clematis will leather flower and vase vine, although most of petals present (Lloyd 1989). Sepals mas- Yyou choose? The myriad of flower these refer to a particular species rather than the querading as petals, sometimes referred to as colors and forms—from the reds, purples and genus as a whole. The generic name Clematis is tepals, vary from four to eight per clematis blues of the large-flowered cultivars to the most often used as the common name. flower. Flower color develops as the buds fully small, waxy yellow Oriental species to the pro- Clematis are mainly woody, climbing open, and sometimes in cooler weather the lific starry-white blossoms of virgin’s bower or plants, but there are herbaceous and nonvining tepals open green and color-up as the blossom sweet autumn clematis—will astound you. species as well. Clematis do not climb by ten- ages (Evison 1991). In some species the seed Your selection will surely be influenced by drils or aerial roots, but instead climb by gently heads are feathery, silver puffballs that cover your ornamental expectation, and should be twining their leaf petioles around nearby sup- the plant later in the season and account for the appropriate for your site and design, but it will ports, including plant stems, branches, wires, common name old man’s beard. most certainly be determined by which clema- small poles and itself. Clematis do not cling to Selecting the right place for clematis in tis you can purchase. Although clematis is walls and without support will ramble until the garden is an important consideration for commonly available to gardeners in some they find something suitable to climb on. In the successful cultivation. Clematis requires a cool, form, not all markets share the wealth of wild, clematis are often found growing at the moist soil for optimum growth. Planting clema- clematis that exists. Garden centers and mail- woods’ edge, where their tops can reach full tis with its crown protected by the shade of a order nurseries are carrying more and more sun and their roots remain in the shade. shrub or tree will provide a cool root zone, as clematis from which you can choose. But An extraordinary diversity of flower col- well as mask the potential bareness of the choosing wisely may not be that simple. ors, sizes and forms occurs in the genus lower stems. Underplanting with a groundcov- Clematis, pronounced klem'e-tis, is a Clematis. Colors range from shades and blends er or perennial will also shade the roots. Do genus in the buttercup family (Ranunculaceae) of blue and red to yellow and white. Flowers not plant clematis where it will have to com- that contains over 300 species native to the can be less than one inch across to over six pete for water, such as too close to a large tree northern and southern hemispheres, and inches wide, and are urn-, bell-, star- or tubular- trunk, in the drier area near a wall or next to a although few of the species are commonly cul- shaped. An interesting floral trait of clematis is building with overhanging eaves. Adequate tivated, many man-made hybrids are found in the presence of colorful, showy sepals and moisture is important and will ensure a healthy the nursery trade. Numerous common names inconspicuous or absent petals. Only in some plant. Clematis can be planted deep and actu- ally benefits from having the crown buried about four inches below the surface of the soil. This practice can assist with regeneration of stems from dormant buds below the soil if the Tom Clark Tom top of the plant is damaged by animals, wilt or mechanical injury. Clematis are commonly placed in three cat- egories based on bloom times, flowering habits and pruning requirements (see sidebar, page 2). There are a number of diseases and pests that can affect clematis in the landscape, with clema- tis wilt being a major and sometimes debilitating disease (see sidebar, page 5). Earwigs, rabbits, mice and slugs can also cause damage. Clematis are effective in a formal or infor- mal landscape, in a natural setting or in a con- tainer on the patio. Plants can be grown in the traditional manner as a focal specimen clam- bering on a wall, fence, trellis or lamp post, or simply allowed to ramble in, over and through other plants. Climbers provide the vertical dimension in small garden spaces while the herbaceous species are wonderful additions to Clematis ‘Ville de Lyon’ in the Pullman Plant Evaluation Garden at the Chicago Botanic Garden 2 Plant Evaluation Notes the perennial border. Weakly climbing or non- microclimates within the garden. A minimum Pruning Requirements vining species like C. ¥ durandii are perfect for of three plants of each taxon were evaluated. rambling through the garden. Many clematis Maintenance practices were kept to a min- Pruning clematis can seem a most daunting species and cultivars can also be used as cut imum to simulate home garden culture. The exercise, but it does not have to be so. Clematis flowers. plants were not fertilized after planting and are routinely placed in three categories to sim- With few demands on the gardener, received supplemental irrigation as needed. A plify the pruning process. Group I includes clematis that flower on short stalks arising clematis will reward you with an abundance mulch of shredded leaves and wood chips was directly from a leaf axil bud, on stems pro- of beautiful blossoms. Combining multiple maintained for aesthetics, water conservation, duced the previous growing season, and there- flower colors or overlapping bloom periods weed control and cooling of the root zone. fore should not be pruned until after flowering will prolong the beauty and elegance of clema- Emerging shoots were tied to plastic coated is finished in the spring (Evison 1991). New tis throughout the season. To see a clematis in wires that were affixed horizontally to the fence stems produced after pruning will eventually full bloom is to understand why it is often at intervals of 12 inches. The natural fiber raffia produce the flower buds for the following called the queen of flowering vines. was used to tie the stems to the wires until the spring. Pruning need only occur if space is lim- leaf petioles could cling naturally. ited or to remove dead and weak stems. Severe Evaluation Project To protect against rabbit damage, each pruning late in the season will affect the next Clematis have been cultivated for centuries, climbing plant was surrounded by a wire mesh year’s crop of flowers. Group I includes the but their popularity as a garden plant dates from cage, 12 to 18 inches tall. Plants were given a earliest-flowering species such as C. alpina, the latter half of the nineteenth century when preventative treatment for clematis wilt when C. macropetala and C. montana. many hybrids were being developed. The British planted in 1990 and again in 1995. The treat- Clematis that produce their first flowers typi- have long grown and hybridized clematis, and ment consisted of a foliar/stem spray and soil cally before mid-June on stems from the pre- in recent years many new hybrids have been drench of Benlate at a rate of one pound per vious season’s wood belong in Group II. introduced from Poland and Japan. Clematis 100 gallons of water. All clematis, except the Pruning should be completed in late winter or growing high into treetops and covering arbors earliest-flowering species, were pruned each early spring when buds begin to swell but and fences are familiar sights in warm climate stems have not yet started to grow. Prune out year in late winter to remove dead stems, zones. But what about clematis in the Midwest? any weak and dead stems, and cut back improve plant vigor and maintain growth with- Indeed,1 we can and do grow clematis in the remaining stems to a pair of strong, healthy in the evaluation space. Stems were typically Midwest, and we’re growing more species and buds. How far back you cut the stems will be cut to within two feet of the ground, but the cultivars all the time. The Chicago Botanic determined by your use. This group will often pruning of each plant was considered individ- flower on new wood again in late summer Garden undertook an evaluation project to deter- ually, based on its health and vigor. Early- or fall. Group II includes the early and mid- mine which clematis were suitable for cultiva- flowering species were pruned only to remove season, large-flowered hybrids like ‘Bees tion in USDA hardiness zone 5b. dead or damaged stems and to aid in training. Jubilee’, ‘Nelly Moser’ and ‘Vyvyan Pennell’. The clematis evaluation project was initi- Group III clematis produce flowers on new ated in the spring of 1990 and continued Observations stems each year, and each stem typically bears through the fall of 1995. The goals were to: The various exposures within the test gar- multiple blossoms. Stems produced in the pre- (1) compare the ornamental characteristics of den created a challenge when observing the vious season usually die during the winter and commercially available species and cultivars; clematis plants and analyzing data collected must be removed before new growth begins in (2) determine the cultural parameters necessary during the trial.