Nothing is more stunning, in my view, than a trellis loaded with bright, colorful clematis flowers. This popular climbing perennial often has the reputation of being difficult to grow. Success is at least partly due to choosing the right variety. With this in mind, Richard Hawke, horticulturist at the Chicago Botanic Garden, recently completed a six-year study evaluating 65 varieties. Each clematis was grown in three locations with different sun exposures. Other than initial soil preparation and annual pruning, maintenance was minimal. Hawke evaluated flower color and size, bloom period, overall coverage of the blooms, winter hardiness, and resistance to disease -- especially to clematis wilt. Based on six years -- data, the following four varieties were Hawke's favorites.
* 'Comtesse de Bouchard', a vigorous climber, reaches more than 8 feet tall in one year. It flowered from mid-June to late August with 5-inch-diameter mauve-pink flowers. During its peak bloom period, flowers covered 80 to 100 percent of the plant. Bloom repeats in October. Comtesse de Bouchard plants had little winter dieback but, in two of the study years, had some dieback from clematis wilt.
* Clematis durandii, is a rambler rather than a climber and is best grown through a shrub or tree, such as arborvitae. In the study, it bloomed abundantly from June through July with 5-inch-diameter indigo flowers; it had some dieback in one year from clematis wilt.
* C. viticella 'Etoile Violette', produced 3-inch-diameter violet flowers that began blooming in late June and continued until August. It also had 80 to 100 percent coverage during peak bloom time and no clematis wilt during the six-year study period.
* 'Ville de Lyon', was noted for its 5-inch-diameter brilliant crimson flowers from late May to July and again in September on vigorous, 7-foot-tall vines. The variety showed no signs of wilt.