Issue 10, 1997 Evaluation Notes 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, and C. macropetala are true your garden, but which clematis will leather and vase , although most of petals present (Lloyd 1989). Sepals mas- Yyou choose? The myriad of flower these refer to a particular rather than the querading as petals, sometimes referred to as colors and forms—from the reds, purples and as a whole. The generic name Clematis is tepals, vary from four to eight per clematis blues of the large-flowered 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 , 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. 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 () of blue and red to yellow and white. 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). , 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 . 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. Many of the clematis were the spring. Stems may live through a mild win- for successful cultivation; and (3) promote the grown in multiple sites with different expo- ter, but plants will become leggy and over- cultivation or use of clematis in northern land- sures. In general, the three plants of a taxon grown if not cut back regularly. As with Group scapes. Sixty-four species and cultivars were grew similarly in each location, with some II, pruning for these plants should be complet- ed in late winter or early spring. Prune the old included in the project (Table 1); all but a few exceptions noted. Site exposures for the rec- growth to a pair of healthy, strong buds near were generously donated by Mr. Raymond J. ommended clematis are noted in Table 2. the base of the plant. Hard pruning will encour- Evison of The Guernsey Clematis Nursery Plants were positioned for optimum exposure age new shoots from the crown. Clematis in Limited, Channel Islands, England. Some of to sunlight, but in several instances clematis this group include the late-flowering, large- the herbaceous species were obtained during a plants became too shaded or crowded by com- flowered cultivars, C. viticella, C. texensis and plant exploration trip to the Republic of Korea panion plants, which ultimately affected the the herbaceous species. or were gifts from other botanical institutions. growth and health of those clematis. Stems should be tied into place immediately The clematis were planted in four types of During the evaluation period, information following pruning. Some degree of labor is sites, providing north-, south-, east- and west- was collected on flower color, size, bloom peri- involved in training clematis onto a structure facing exposures. The sites were fairly similar od and overall coverage; plant height and form; or into a large plant. Many clematis grow in character with the exception of the specific disease and pest resistance; plant health; winter so quickly in the spring that daily attention exposure. Soils were a clay loam with shred- hardiness; and cultural adaptability. Sixty of to training is helpful. Initial care in training ded leaves and wood chips added; no addition- the original 64 taxa completed the six-year pro- will reward you with a better display. Plastic- al soil amendments were made at the time of ject. A summary rating was assigned to each coated wire or mesh will support the clematis on a wall or fence. Clematis need to reach planting. Soils were well-drained in each loca- taxon based on its overall performance and a horizontal or vertical support about every six tion with an average pH of 7.4 during the eval- health (Table 1). The 33 clematis that are rec- inches. Gaps of greater distance are accept- uation term. Climbing plants were grown on ommended for northern landscapes are cited able if plants are aided in climbing during the wooden fences, ranging from five to seven feet in Table 2, with a check mark signifying supe- early season. tall. The configuration of the fence system and rior performances. Taxa that received fair to the companion plantings created a variety of poor ratings are not included in the table as Plant Evaluation Notes 3

Table 1: Clematis Evaluation Group they are generally not recommended. A dis- tal traits, vigorous habits, winter hardiness and and Summary Ratings cussion of plant health, diseases, pests and win- disease and pest resistance (Table 2). Some ★ aethusifolia ter hardiness follows the general observations. characteristics may have been stronger or weak- ★★ alpina ‘Constance’ Observations are based on how a plant er in a particular year, but the overall display ★★★ alpina ‘Pamela Jackman’ grew in a specific site and may not be exact for was consistently good. ★★ alpina ‘Willy’ the same plant grown under different condi- Flower coverage was usually noted in the ★★ ‘Asao’ tions. Nearly all of the taxa had one or more 60% to 80% range, although coverage was ★★★ ‘Ascotiensis’ plants growing in a south-facing position, recorded as high as 100%. Heavy flower produc- ★★★ ‘Barbara Jackman’ ★★★★ ‘Bees Jubilee’ although sixteen taxa had no representative tion was not always enough to overcome a lesser ★★★ ‘Bill Mackenzie’ plants in a southern exposure, including trait. ‘Perle d’Azur’ had consistently high flower ★ campaniflora C. alpina ‘Willy’, ‘Ascotiensis’, C. fremontii, coverage, but its habit was rather loose and leggy. ★★★★ ‘Comtesse de Bouchaud’ ‘Gillian Blades’, ‘Gipsy Queen’, C. koreana, Clematis serratifolia was one of the most vigor- ★★★ ‘Countess of Lovelace’ ‘Lasurstern’, ‘Lilacina Floribunda’, ‘Perle ous and floriferous species, but brown leaves ★★★ x cylindrica d'Azur’, C. recta, ‘Rouge Cardinal’, were typically observed throughout the plant and ★★ ‘Duchess of Edinburgh’ C. trichotoma, C. viticella ‘Alba Luxurians’, concentrated on the lower portion of the stems. Its ★ ‘Duchess of Sutherland’ ★★★★ x durandii C. viticella ‘Etoile Violette’, C. viticella habit and growth rate were rampant and weedy, ★★★ ‘Elsa Späth’ ‘Grandiflora Sanguinea’ and C. viticella ‘Polish spreading by seeds and rhizomes. ★★★ ‘Ernest Markham’ Spirit’. Of these, C. alpina ‘Willy’, ‘Gillian For sheer beauty of blossom, seven taxa ★★ ‘Etoile de Malicorne’ Blades’, ‘Lasurstern’ and ‘Lilacina Floribunda’ were outstanding, including ‘Ascotiensis’, ★★ ‘Fair Rosamond’ grew weakly in the other exposures. ‘Ernest Markham’, ‘Guernsey Cream’, ‘Lady ★ florida ‘Alba Plena’ Nine taxa received superior ratings for Betty Balfour’, ‘Marie Boisselot’, ‘Perle ★ florida ‘Sieboldii’ ★★ fremontii heavy flower production, high quality blossoms, d’Azur’ and ‘Rouge Cardinal’. In fact, these ★ ‘Gillian Blades’ exceptional ornamental characteristics, vigor- flowers were among the most significantly dec- ★★★ ‘Gipsy Queen’ ous habits, winter hardiness and disease and orative of the entire evaluation project. Clear ★★ glauca var. akebioides pest resistance (Table 2). These plants were also white sepals and white gave ‘Marie ★★★ ‘Guernsey Cream’ rated highly because plant health and vigor Boisselot’ a clean appearance; it was the best ★★★ ‘Hagley Hybrid’ increased each season. white-flowered in the trial. The bright ★★ ‘Henryi’ The large-flowered hybrids—‘Bees blue flowers of ‘Ascotiensis’ were vibrant, espe- ★★★★ x jouiniana ‘Praecox’ ★ ‘King Edward VII’ Jubilee’, ‘Comtesse de Bouchaud’, ‘Ville de cially in the cool shade of morning; unfortu- ★★ koreana Lyon’ and ‘Vyvyan Pennell’—had exceptional nately, the brown, spent flowers sometimes ★★★ ‘Lady Betty Balfour’ floral displays. Flower coverage was consis- ★★ ‘Lasurstern’ tently high at 80% to 100% with peak coverage ★★ ‘Lilacina Floribunda’ lasting for over six weeks. Individual blossoms ★★★★ macropetala typically remained ornamental for 9 to 11 days. ★★★ ‘Marie Boisselot’ Clematis ¥ durandii topped the list for dura- ★★★ ‘Madame Baron Veillard’ ★★ montana ‘Grandiflora’ tion of ornamental effect of individual flowers ★★★ ‘Mrs. Cholmondeley’ with an average of 17 days.1 ★★★ ‘Mrs. P.B. Truax’ With the exception of the bushy habit of ★★★ ‘Nelly Moser’ ‘Bees Jubilee’, most of these clematis were ★★★ ‘Pagoda’ vigorous climbers. Some plants grew so quick- ★★★ ‘Perle d’Azur’ ly that assiduous attention to training was cru- ★★ pitcheri ★★★ recta cial each spring. When left unattended, plants ★ ‘Richard Pennell’ mounded on themselves, resulting in inferior ★★★ ‘Rouge Cardinal’ forms. Clematis ‘Ville de Lyon’, C. viticella ★★★ serratifolia ‘Etoile Violette’ and C. viticella ‘Grandiflora ★★ texensis ‘Duchess of Albany’ Sanguinea’ were typically bare at the base, to ★★ texensis ‘Gravetye Beauty’ about three feet. Clematis ¥ durandii was a ★★ texensis ‘Sir Trevor Lawrence’ nonclimbing hybrid best left to clamber along ★★★ ‘The President’ ★★★ tibetana the ground. When treated like a vine and tied ★★ trichotoma to the fence, its 12-inch-long internodes made ★★★★ ‘Ville de Lyon’ an open display. The mounded habit and ram- ★★ viticella ‘Alba Luxurians’ bling stems of C. ¥ jouiniana ‘Praecox’ ★★★★ viticella ‘Etoile Violette’ worked well cascading over a retaining wall. ★★★★ viticella ‘Grandiflora Sanguinea’ Although not a climber, it made a passable dis- ★★ viticella ‘Little Nell’ play when tied up to the fence. ★★ viticella ‘Polish Spirit’ ★★ viticella ‘Purpurea Plena Elegans’ Twenty-four taxa received high ratings for ★★★★ ‘Vyvyan Pennell’ flower production, blossom quality, ornamen- ★★ ‘William Kennett’ 1 Only Clematis florida ‘Alba Plena’ surpassed this mark with flowers Summary Performance Ratings: lasting an average of 31 days, and with one flower remaining ★★★★ Excellent, ★★★ Good, ★★ Fair, ★ Poor ornamental for 62 days in 1994. Plant Evaluation Notes 4 hung onto the plants. The velvety crimson blos- of the fence to hold its heavy mass. ‘Polish Spirit’ was 100% in 1991 but only soms of ‘Rouge Cardinal’ were among the most Under half of the evaluation group reached 40% in subsequent years. This dra- beautiful of all. received fair to poor ratings due to one or more matic decline in flower production put ‘Polish Color was just one of the floral charac- of the following reasons: low flower produc- Spirit’ behind some of the other C. viticella teristics noted. All plants of ‘Hagley Hybrid’ tion, inferior habit, decreased plant vigor and cultivars even though it sustained a healthy and were grown in full sun, which faded out the health, foliar problems and diseases. Clematis vigorous habit. Clematis with flower coverage delicate pink flowers. Its crinkled, crepe paper- that received fair ratings included C. alpina of 40% to 60% but with weak or inferior plant like blossoms were particularly attractive on ‘Constance’, C. alpina ‘Willy’, ‘Asao’, habits were ‘Asao’, C. glauca var. akebioides, cloudy days or in low light. ‘Mrs. P.B. Truax’ Duchess of Edinburgh’, ‘Etoile de Malicorne’, ‘Lilacina Floribunda’, C. viticella ‘Alba held its flowers in a tier above the foliage, thus ‘Fair Rosamond’, C. fremontii, C. glauca var. Luxurians’ and C. viticella ‘Purpurea Plena displaying the blossoms in a more distinct akebioides, ‘Henryi’, C. koreana, ‘Lasurstern’, Elegans’. And the clematis that exhibited both manner. Flower production was usually high ‘Lilacina Floribunda’, C. montana low flower production and inferior habits were for C. tibetana, but in some years its full ‘Grandiflora’, C. pitcheri, C. texensis ‘Duchess C. alpina ‘Willy’, ‘Lasurstern’, C. pitcheri, potential was not realized because the late-sea- of Albany’, C. texensis ‘Gravetye Beauty’, C. texensis ‘Sir Trevor Lawrence’ and son flowers were killed by frost. C. texensis ‘Sir Trevor Lawrence’, C. viticella ‘Little Nell’. The plant vigor, health and habits of taxa C. trichotoma, C. viticella ‘Alba Luxurians’, Several taxa that received fair ratings also in this group were also typically good with a C. viticella ‘Little Nell’, C. viticella ‘Polish exhibited inferior floral quality. ‘Duchess of few exceptions observed. Dead stems were Spirit’, C. viticella ‘Purpurea Plena Elegans’ Edinburgh’ and C. viticella ‘Alba Luxurians’ sometimes an aesthetic problem on the early- and ‘William Kennett’. both had white flowers with a green, leafy flowering C. alpina ‘Pamela Jackman’. Since Aside from disease and other health prob- character. Sepals were often distorted and these plants were not cut back each spring, lems, the most notable reasons that plants puckered at the margins and hung onto the greater attention to cleanup was required later received fair ratings were low flower produc- plants after turning brown. The lavender-blue in the season or the plants became messy. The tion and inferior plant habits. The clematis taxa flowers of ‘William Kennett’ were often short stems of Clematis ¥ cylindrica twined that rated low in flower production, less than washed-out and lost among the foliage. together and only weakly climbed up the fence. 40% coverage, were ‘Etoile de Malicorne’, Clematis trichotoma was a vigorous plant that ‘Guernsey Cream’was an early-flowering ‘Fair Rosamond’, C. fremontii, ‘Henryi’, C. never flowered. Group II hybrid that produced abundant blos- koreana, C. montana ‘Grandiflora’, C. texensis Fair-rated plants are not usually recom- soms on old wood. ‘Lady Betty Balfour’ was ‘Duchess of Albany’, C. texensis ‘Gravetye mended, but there were a few that showed so vigorous that it quickly outgrew the evalua- Beauty’, C. trichotoma and C. viticella potential for increased vigor and health if grown tion space and required extra support at the top ‘Polish Spirit’. Flower coverage on C. viticella in a different setting or given more cultural care.

✓ ✓ ✓ ✓ ✓ Recommended Clematis for Northern Table 2: ✓ ✓ ✓ ✓ ✓

viticella viticella tibetana serratifolia recta macropetala alpina ‘Bees Jubilee’ Jackman’ ‘Barbara Clematis Ms P.B. Truax’‘Mrs. Mdm ao elad oyllc lgtycpe 11.4-12.7 (4 cm slightly cupped rosy-lilac, ‘Madame Baron Veillard’ Pgd’pl upe odn . m (1 3.2 cm nodding purple, pale President’ ‘The ‘Pagoda’ ‘Nelly Moser’ ‘Ville de Lyon’ bright crimson red 10.2-12.7 cm (4-5 in) late May-late Jul, Sep-Oct 80-100% >2.1 m (7 ft) >2.1 m (7 ft) 80-100% Sep-Oct late May-late Jul, 10.2-12.7 (4-5 in) cm 16.5-17.8 (6 cm double/single lavender-blue, crimson red bright Pennell’ ‘Vyvyan Lyon’ ‘Ville de ¥ RueCria’dr e 11.4-12.7 (4 cm 2 1 Superior performance 14.0-15.2 dark red (5 11.4 (4 cm cm ‘Rouge Cardinal’ Cholmondeley’ ‘Mrs. blue magenta ‘ ‘Ernest Markham’ ‘Elsa Späth’ ¥ Mackenzie’ ‘Bill MreBislt ht 521. m 67i)eryJnlt u,AgSp 08%>2.4 m (8 ft) 60-80% Aug-Sep early Jun-late Jul, 15.2-17.8 (6-7 in) cm white ‘Marie Boisselot’ PredAu’bu 1. m 4i) aeJnlt u,SpOt 010 >2.4 m (8 ft) 60-100% Sep-Oct late Jun-late Jul, >2.4 m (8 ft) >1.8 m (6 ft) (4 in) 10.2 cm 60-90% 50-80% Sep-Oct mid Jun-early Aug, mid Jul-late Sep (5 in) 12.7 cm 10.1-12.7 (4-5 in) cm blue 11.4-12.7 (4 cm 11.4‘Perle (4 d’Azur’ cm (5 14.0 cm dark purple purple creamy-yellow Balfour’ ‘Lady Betty ‘Guernsey Cream’ ‘Gipsy Queen’ edges ruffled lilac-blue, mauve-pink ¥ ‘Countess of Lovelace’ ‘Comtesse Bouchaud’ de ‘Ascotiensis’ alyHbi’pn,ceepprlo 011. m 46i)mdJneryAg e 08%>2.4 m (8 ft) 60-80% Sep mid Jun-early Aug, 10.1-15.2 (4-6 in) cm crepe paper look pink, Hagley Hybrid’

eotn rrpa lo eidi oe fe h om.Remontant is defined as a nonflowering weeks f period of at least two Remontant or repeat the comma. bloom period is noted after egtrnentda rae hn()o esta <.Size based on existing evaluation location with the potential for growi Height range noted as greater than (>) or less (<).

jouiniana durandii cylindrica ‘Pamela Jackman’‘Pamela GadfoaSnuna epmgna89c (3 8.9 cm magenta deep ‘Grandiflora Sanguinea’ Landscapes ‘Etoile Violette’ ‘Etoile Pacx ht n lih lsee . m (1 3.8 cm clustered white and bluish, ‘Praecox’ aedr togvoe a 271. m 56i)eryJneryJl u-c 08%>1.8 m (6 ft) 60-80% Aug-Oct early Jun-early Jul, 14.0-15.2 (5 cm 12.7-15.2 (5-6 in) cm darker bar mauve-pink, violet strong bar lavender, lavender-blue 14.0 cm (5 pale mauve, carmine bar 15.2 cm (6 in) late May-early Jul, Sep 60-80% >2.1 m (7 ft) >2.1 m (7 ft) 60-80% (5 14.0 cm Sep late May-early Jul, (6 in) 15.2 cm rich purple bar carmine pale mauve, iltprl 8.9-10.2 (3 cm violet-purple (3 8.9 cm blue deep ht,sar . m 1i)lt a-al u 6-0 0.9 m (3 ft) 60-80% >1.5 m (5 ft) late May-early Aug 60-80% (1 3.2 cm (1 3.2 cm in) (1 2.5 cm Aug-Sep early Jun-late Jul, 1.5 m (5 ft) (5 in) 12.7 60-80% cm >0.9 m (3 ft) (1 3.2-3.8 cm 80% bell-shaped yellow, Aug-Sep mid Jun-late Jul, nodding yellow, starry white, (5 in) 12.7 cm mid Jun-early Aug lavender-blue (1 3.8 cm lavender (1-2 in) 2.5-5.1 cm indigo-blue tepals recurving purplish-blue, sulfur yellow rgtbu 11.4-14.0 (4 cm blue bright lwrClrCaatrFoe ieBloom Period Flower Size Flower Color/Character 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 / / / / / / / / / / / / / / / / / / / / / 2 2 2 4 2 4 2 4 2 2 4 2 2 2 2 2 2 2 2 2 2 -7 in) late May-Aug, Sep-Oct 60-100% >2.1 m (7 ft) >2.1 m (7 ft) >2.4 m (8 ft) 60-100% 80-100% >1.8 m (6 ft) Sep-Oct late May-Aug, Sep mid Jun-late Aug, 60-80% >1.8 m (6 ft) -7 in) -4 in) 60-80% Aug-Sep early Jun-late Jul, >1.5 m (5 ft) -5 in) >1.8 m (6 ft) 80% mid Jul-mid Aug 60-80% -5 in) Sep -1 late May-mid Jun, <1.8 m (6 ft) early Jun-mid Aug -5 in) 60-100% -6 in) Jul-Aug late May-late June, -6 in) -5 n aeJnmdAg e-c 010 >3.7 m (12 ft) >2.7 m (9 ft) >2.1 m (7 ft) 80-100% >1.8 60-80% m (6 ft) >2.1 m (7 ft) 80-100% 60-80% Sep-Oct late Jun-mid Aug, 60% >2.4 m (8 ft) late Sep-Oct (frost) Aug-Sep early Jun-late Jul, in) mid Aug-mid Sep 60-80% 1.2 m (4 ft) in) in) Sep mid Jun-Aug, in) >2.1 m (7 ft) 60-100% Aug late May-late Jun, 80-100% in) >4.6 m (15 ft) in) >1.8 m (6 ft) early Jul-early Sep >2.4 m (8 ft) 60-80% 60-80% mid Jun-late 80-100% Aug in) >1.5 m (5 ft) Aug early Jun-late Jul, in) Sep-Oct mid Jun-late Aug, 80% mid July-Oct in) in) Aug-Sep early May-late May, in) in) 1 1 / ng larger if given more space. / 2 2 n al a-al u,JlAg 010 >1.5 m (5 ft) 80-100% Jul-Aug early May-early Jun, in) n lt u-aeAg e-c 5-0 >1.8 m (6 ft) 50-80% Sep-Oct late Jun-late Aug, in) ollowing bloom period. the primary 1 3 denoted by denoted Good performance in respectively. east and west exposure, south, Refers to the general performance of a plant or plants in a north, oeaeN S E W Groups N S E W Coverage Flower Plant Height ■ ; a lesser performance in a specific by exposure denoted 2 Exposure ■■ ■ ■■ ■ ■■ ■ ■ ■ ■ ■■ ■■ ■ ■ ■■ ■ ■ ■■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■■ ■ ■■ ■ ■ ■■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 3 ■ . Boldface denotes taxa with ornamental . Pruning Pruning 2 not a strong climber; not a strong dark green leaves 2 old flowers hang on brown; wilt in to 50% 1993-95 3 2 not a strong climber; not a strong chlorosis noted each year 2 3 compact, not a strong climber; not a strong minor chlorosis compact, 3 vigorous climber; chlorosis noted in 1995 3 flowering not cut back until for do after best results 2 best white clematis tested; minor wilt in 1993,1995 2 potentially weedy; spreads by seed and rhizomes 3 good climber; minor chlorosis in 1994; wilt in 1995 good climber; flowers held away from plant 2 2 vigorous climber; minor chlorosis noted each year 3 herbaceous; blue-green leaves; rabbit damage 3 nonclimber; long-lasting flowers; wilt 1994-95 climber; not a strong twines upon itself 3 3 vigorous plants; minor wilt noted in 1991 vigorous and floriferous;2 stems bare at base 3 minor wilt noted good climber;1994-95 chlorosis, 2 climber; not a strong flowers can hang on brown 2 foesfd nsn io it chlorosis 1994-95 flowers fade in sun; minor wilt, 3 odcibr hr-ie lwr,4 days only good climber; flowers, short-lived 1 3 vigorous plant; long internodes; bare stems at vigorous plant; long internodes; base 3 noted in anthracnose 1994 vigorous climber; wilt, 3 vigorous climber; minor chlorosis noted in 1994 3 stems burgundy; increased in vigor each year 3 glaucous leaves; killed flowers often by frost noted in purple stems; anthracnose 1992 and 1994 3 2 3 purple stems nonclimber; leaves hold brown over winter 3 3 vigorous strong habit, good climber; wilt noted at in 25% to 50% 1995 rarely injured overwinter; wilt noted in 1993-95 climber 2 vigorous climber; one of the best fruit displays 3 3 fruit from July ornamental to September 1 Comments a specific exposure 5 Plant Evaluation Notes

plants of C. campaniflora, C. florida ‘Alba Clematis Wilt Plena’ and C. florida ‘Sieboldii’ died from lack by Andra Windorf Nus, former research assistant. of winter hardiness. Current address: Plant Recorder, Longwood Gardens, P.O. Box 501, Kennett Square, PA 19348. Plant Health, Diseases and Pests and Richard Hawke Winter Hardiness Wilt is a confusing problem affecting clematis. Plant health, affected by disease and cul- Conclusive research on the cause of clematis wilt tural conditions, varied among plants in the col- is unavailable, and little is known about the rela- tive success of recommended prevention and lection. In some cases, the decline in health was control methods. progressive over the course of the evaluation term, and in other instances, plant health Jim Fisk, a respected clematis expert, believes declined quickly in one season. A variety of that clematis wilt “is not a disease at all but a failure of the very thin stem to cope with a sud- health issues, diseases and pests afflicted the den demand for moisture from the stem leaves clematis collection, but many plants were unaf- and flowers,” resulting “in a breakdown of the fected or recovered from injury. tissues at a certain spot.” Other experts, however, Nutrient deficiency expressed as interveinal Clematis ‘Bees Jubilee’ agree that the symptoms are probably caused by chlorosis was not a significant ornamental or a fungus, but which fungus it might be is also health problem for the majority of clematis. debated. Ascochyta clematidina, the most com- Chlorosis on individual plants was observed in 1994. At that time the following clematis were monly accepted cause, has been identified both some years, yet was absent or inconsequential in infected with wilt at low levels: ‘Ascotiensis’, in the United States and Great Britain. Another ¥ fungus, Coniothyrium clematidisrectae, has been other years. It was, however, a significant health ‘Countess of Lovelace’, C. cylindrica, identified in Holland as a possible cause of wilt, concern and a limiting factor to the ornamental C. ¥ durandii, ‘Elsa Späth’, ‘Ernest Markham’, and Barry Fretwell in his book Clematis notes quality of all plants of ‘Asao’, ‘Duchess of ‘Hagley Hybrid’, ‘King Edward VII’, ‘Lady that “it is fairly widespread, and whether this, or Edinburgh’, ‘Duchess of Sutherland’, ‘Gillian Betty Balfour’, ‘Marie Boisselot’, ‘Madame a combination of the two (fungi), is to blame we Blades’, ‘King Edward VII’ and ‘Lasurstern’. Baron Veillard’, ‘Nelly Moser’, C. texensis have yet to find out.” Chlorosis was less severe but observed on ‘Elsa ‘Duchess of Albany’, C. texensis ‘Gravetye Clematis wilt is most damaging during the early Späth’, ‘Fair Rosamond’, ‘Gipsy Queen’, ‘Hagley Beauty’ and ‘William Kennett’. Wilt rarely growing season, when the plants are in bud or Hybrid’, ‘Henryi’, ‘Madame Baron Veillard’, killed more than 25% of a plant’s stems at any flower. Leaf spot and/or partial stem rot occurs, ‘Mrs. Cholmondeley’, ‘Nelly Moser’, ‘Rouge time, with most plants recovering fully from and the vine wilts and withers because moisture Cardinal’, C. trichotoma and ‘William Kennett’. the infection. But one plant each of the follow- does not reach the growing tips. This can happen Plants that had inferior health, vigor or ing clematis was greatly weakened by wilt over slowly or quickly, to one stem or to the entire plant. Fungicides have been used as a preventa- reduced flower production due to competition or the course of the trial: ‘Comtesse de tive; however, once the plant has been infected, shade were ‘Duchess of Sutherland’, Bouchaud’, ‘Duchess of Edinburgh’, ‘Duchess the only recommended control is to prune out C. fremontii, C. koreana, C. viticella ‘Alba of Sutherland’, ‘Etoile de Malicorne’, ‘Henryi’, affected stems below the infection point. Luxurians’, C. viticella ‘Little Nell’ and ‘Madame Baron Veillard’, ‘Perle d'Azur’ and C. texensis ‘Gravetye Beauty’. Only four plants It appears most probable that clematis wilt is C. viticella ‘Purpurea Plena Elegans’. Clematis caused by a fungus that attacks the vine, causes fremontii in particular was healthy with moderate died following repetitive years of severe injury brown leaf spotting and/or stem rotting, where- growth, but was planted in too much shade to from clematis wilt – one plant of ‘Duchess of upon the vine wilts for lack of water. Experts do produce abundant flowers. Clematis plants that Sutherland’ and three plants of ‘Henryi’. seem to agree that clematis wilt is usually not were never strong or healthy included Anthracnose was first observed in the fatal, and most plants will resprout from below ‘Lasurstern’, ‘Lilacina Floribunda’ and clematis collection in early August of 1993 the infected point – some even after three years C. pitcheri. These plants did not gain vigor after and was confirmed by the University of of being presumed dead. planting and remained loose and spindly in habit. Illinois Plant Clinic, Urbana, Illinois. A few diseases and pests were observed, Symptoms of the disease, caused by the fun- with varying degrees of injury noted from gus Glomerella cingulata, were necrotic spot- Clematis that ranked between fair and good clematis wilt and anthracnose to earwigs and ting of leaf margins, stem blight and leaf drop, included C. fremontii, C. texensis ‘Duchess of rabbits. Clematis wilt was the most serious dis- typically observed in the fall. Anthracnose was Albany’, C. texensis ‘Sir Trevor Lawrence’, ease problem and was indicated by the decline evident again in 1994 and 1995 on clematis. C. trichotoma, C. viticella ‘Alba Luxurians’, of leaves and stems above the point of infec- There was no exclusive cultural condition, C. viticella ‘Little Nell’ and C. viticella tion, usually near the base of the plant. Stems exposure or site-type in which anthracnose was ‘Purpurea Plena Elegans’. withered and died, either slowly or rapidly. observed. It affected healthy plants, as well as Only eight clematis performed so poorly Symptoms were usually observed from early weak or unhealthy plants. Although the severi- that no recommendation can be given. In each June onward, as the large-flowered clematis ty of infection varied, no plants were killed. case, ornamental quality was so diminished were beginning to bloom (see sidebar, left). Taxa with one or more plants affected by and/or disease problems too severe for the Wilt was first observed in 1992 on one anthracnose included ‘Bees Jubilee’, plants to be successfully grown. Clematis that plant each of ‘Duchess of Sutherland’, ‘Etoile ‘Comtesse de Bouchaud’, ‘Duchess of declined steadily in plant health and received de Malicorne’ and C. texensis ‘Gravetye Edinburgh’, C. ¥ durandii, ‘Elsa Späth’, ‘Etoile the lowest ratings were C. aethusifolia, Beauty’. Occurrences of wilt in subsequent de Malicorne’, ‘Fair Rosamond’, ‘Hagley ‘Duchess of Sutherland’, ‘Gillian Blades’, years were sporadic and varied in degree of Hybrid’, ‘King Edward VII’, ‘Lady Betty ‘King Edward VII’ and ‘Richard Pennell’. All injury, with no significant infection noted until Balfour’, ‘Mrs. P.B. Truax’, ‘Perle d’Azur’, 6 Plant Evaluation Notes Tom Clark Tom Richard Hawke Richard Hawke

Clematis ‘Lady Betty Balfour’ Clematis ‘Guernsey Cream’ Clematis ¥ durandii

C. serratifolia, C. texensis ‘Duchess of because of the loss of the older stems, but the be a frustrating disease because it strikes just as Albany’, C. texensis ‘Sir Trevor Lawrence’, new growth was always vigorous, exceeding the plant begins to bloom, but it is rarely fatal ‘The President’, ‘Ville de Lyon’, C. viticella eight feet in a season. Clematis that did not and plants generally regenerate quickly. At this ‘Alba Luxurians’, C. viticella ‘Etoile Violette’, complete the full six-year evaluation term due time sulfur is the only product labeled for the C. viticella ‘Grandiflora Sanguinea’, to winter injury included all plants of C. cam- treatment of clematis wilt, and removal of dis- C. viticella ‘Little Nell’, C. viticella ‘Purpurea paniflora, C. florida ‘Alba Plena’, C. florida eased plant parts is an important practice in the Plena Elegans’ and ‘William Kennett’. ‘Sieboldii’ and ‘Richard Pennell’. Both culti- control of wilt. There is no chemical labeled for Damage from insects and animals was vars of Clematis florida survived two winters the treatment of anthracnose, so sanitation is the less notable than injury from wilt and anthrac- but were greatly weakened and eventually died best prevention here. Pests were insignificant nose. Earwigs were an aesthetic nuisance only. in the third growing season. overall, and rabbits proved only a minor nui- This nocturnal insect chewed holes in flower sance that were effectively controlled by placing Conclusions buds and along the edges of tepals, sometimes wire mesh cages around the base of the plants. Clematis are good choices for northern leaving the flowers tattered. Damage was Be creative with clematis. Take advan- landscapes. With attention to cultural conditions, observed in most years but varied in degree of tage of the many flower forms and colors by site placement and plant selection, you will be severity. Mainly large-flowered varieties grow- combining more than one clematis for inter- rewarded with exceptional floral displays. Over ing in a southern exposure were damaged. esting effects and a prolonged bloom display. half the clematis evaluated completed the project Injury from rabbits was insignificant because Remember that there is a clematis for just with good to excellent ratings. Exceptional plant of the protective mesh cages surrounding most about any situation, whether to cover an arbor, vigor, health and floral characteristics were plants. The stems of were not climb a pole or ramble through the garden bor- notable attributes that set this group apart from protected, and consequently these plants der. Choose wisely, and be rewarded with the remainder of the test collection. incurred some damage. Feeding injury was extravagant blossoms for many years. ❦ Exposure did not appear to be a critical also noted on a few other plants where the factor for most clematis, but the best results mesh cage was less than 15 inches tall. were seen in south-facing positions. The major- References Stem dieback due to winter injury was not ity of clematis had at least one plant facing Evison, R. J. 1991. Making the Most of considered important unless notably severe, Clematis, 2nd Ed. Wisbech, England: south, and most of these plants were healthy, since most clematis were routinely cut back Burall Floraprint. vigorous and floriferous, gaining in stature each each spring to control size and to remove dead season. Providing shade for the base of the plant Fisk, J. 1991. Clematis. London: stems. Stem hardiness varied among taxa and Cassell Publishers Limited. helped moderate the soil temperature and retain with each year, and no consistent injury was the necessary soil moisture. Too much competi- Fretwell, B. 1989. Clematis. Deer Park, observed on any of the taxa. Plants that were tion limited the growth of some plants, but most WI: Capability’s Books. weakened by winter injury in the first two years clematis mixed well with their companions and and never returned to full health included C. Lloyd, C. 1989. Clematis. Deer Park, usually held their own in the garden. WI: Capability’s Books. aethusifolia, C. glauca var. akebioides and C. Clematis wilt and anthracnose were pitcheri. The stems of C. montana ‘Grandiflora’ observed at various levels, and except in a few were typically killed to the base of the plant cases, were not devastating. Clematis wilt can over winter. Flowering was low and sporadic

Financial support for this publication from the Searle Research Program, the Helen V. Froehlich Foundation Research Initiative and the Green Partnership is gratefully acknowledged. We deeply appreciate the generous contribution of plants for the clematis project from Raymond J. Evison, The Guernsey Clematis Nursery Limited, England, and offer a special thanks to Tom Clark, Lynette Rodriguez and Andra Windorf Nus for their help in collecting data in 1992, 1993 and 1994, respectively.

Plant Evaluation Notes© are periodic publications of the Chicago Horticultural Society. For more information or copies of back issues, contact the Plant Evaluation Program, Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, Illinois 60022. The Chicago Botanic Garden is owned by the Forest Preserve District of Cook County and operated by the Chicago Horticultural Society.

CBG 10M 5/97