Extension Educator, Horticulture
I'm not sure who was involved in the coronation, but clematis has been crowned queen of the flowering vines. Certainly clematis in full bloom is a sight worthy of nobility. Clematis offer tremendous variety with more than 300 species in the genus Clematis.
Although our midwestern tongues blurt out klem-a'tis, the correct pronunciation is actually klem'-e-tis with the accent on the first syllable. I came across an excellent article written by Richard Hawke of the Chicago Botanic Garden summarizing a clematis evaluation study conducted at the garden from 1990 to 1995.
First, Hawke offered these tips for successful clematis growing: Clematis require a cool, moist and well-drained soil. Plant clematis where the root zone is mulched and receives shade from a shrub, tree, ground cover or perennial plant. The vines enjoy some sun, but appreciate late afternoon shade. Avoid extremely hot sunny areas and extremely wet conditions.
High pH soils of 6-7.5 are often recommended, but woody plant expert Michael Dirr states he personally believes they are not pH sensitive and will survive even at a pH of 4.5.
Clematis can be planted deep and actually benefit from having the crown buried about four inches below the soil surface. According to Hawke this practice can assist in production of stems from dormant buds below the soil if the top of the plant is damaged by animals, wilt or mechanical injury. One serious problem with clematis is wilt. I have noticed it often after the first hot dry day early in the growing season. Although there is conflicting information as to the exact cause, the most commonly listed is a fungus. Evidently a stem rot occurs, and the vine quickly browns because little moisture reaches the growing tips. The good news is the wilt generally kills less than 25 percent of the stems and is rarely fatal. Most plants will resprout.
A sulfur fungicide can be used as a preventative. However the leaves and stems should be sprayed thoroughly at 7-10 day intervals during rainy spring weather and early summer weather. Of the 64 different species and cultivars trialed, the following showed excellent performance in flowering, vigorous habit, winter hardiness and insect and disease resistance.
'Bees Jubilee' - mauve pink 5 1/2 to 6 inch flowers; late May - late June and again in July- August; not a strong climber; bushy habit; fruits ornamental.
'Comtesse de Bouchaud' - mauve pink 4 1/2 inch flowers; mid June-late August and September- October; vigorous and free flowering; rarely injured over winter but some wilt problems.
x durandii - indigo blue 5 inch flowers; mid June-late July and August-September; non climber; long lasting flowers; some wilt problems. x jouiniana 'Praecox' - white and bluish clustered 1 2 flowers; early July-early September; nonclimber; nice cascading over a retaining wall.
macropetala- lavender 1 1/4-1 1/2 inch flowers early May-early June and July-August; good climber; individual flowers last only 4 days; fruits ornamental.
'Ville de Lyon'- crimson red 4-5 inch flowers; late May-late July and September-October; exceptional flower display; vigorous climber.
viticella 'Etoile Violette' violet purple 3 1/2-4 inch flowers; mid June-late August and September; vigorous and floriferous; stems bare at base up to 3 feet; fruits ornamental.
viticella 'Grandiflora Sanguinea' - deep magenta 3 1/2 inch flowers; late June-mid August and September-October; stems burgundy.
U of I Extension - Champaign County is offering a home study course "Stepping Stones to Perennial Garden Design." The six lessons are designed to help the new gardener evaluate their landscape, select a garden site, and follow a step-by-step approach to creating a perennial garden. The first four sessions are mailed each week starting April 12. On May 12 at 7:00 pm at the Extension auditorium, participants will learn about perennial plant selection. Mail $7 to the U of I Extension - Champaign County.