Growing and Pruning Clematis

Perennial flowering vines add height and diversity to the garden. They are valuable for adding vertical interest to the garden, whether draping a trellis, growing within a tuteur, or planted at the base of a shrub, gracefully winding along the branches. One of the most readily available and highly popular vines found in local gardens are Clematis species. They earn the moniker "queen of the vines" because varieties can be found that bloom from early spring to late fall. Some are smothered in clouds of tiny, delicate flowers, while others sport blossoms up to 8 inches in diameter.

The most problematic issue with clematis is the fungal clematis wilt, which can lead to the death of the vine. Information on diseases of clematis is reviewed in an article from Penn State Extension. When purchasing a clematis from a nursery or via mail order, look for mildew-resistant selections. Clematis wilt primarily affects the large flowering hybrids, especially early flowering Group 2 hybrids described below. If you have had recurring issues with wilt, consider investing in a small-flowered Clematis viticella hybrid. They are more resilient, withstand windy conditions, and most are wilt-resistant.

With proper planting and care, clematis will thrive. Clematis prefer full sun and well-drained, organic soil with a neutral to slightly alkaline pH. Conduct a soil test before planting and adjust the pH as needed. Plant clematis deeper than normal with at least two pairs of opposite buds buried below soil level. Gently angle the stem of the plant so that the buds can easily be set below ground level without damage to the stem. When planted this way, clematis will develop a sturdier root system and may recover more readily if afflicted with stem wilt.

Keep the soil around the roots cool by mulching or planting shallow-rooted perennials or annuals at the base of the vine to shade the roots and keep the soil from drying out. When irrigating, water the soil rather than the foliage to prevent potential disease issues. Provide adequate support immediately after planting to minimize stem injury.

There are three groupings or types of clematis, organized by their pruning and cultivation requirements. If you know the name of your clematis, you can look it up. If not, take an educated guess based on when plants flower and the appearance of buds on the vine as they break winter dormancy.

Lee Reich, horticulturist and author, states: "If you are still not sure what type of clematis you have or which group it belongs to, let the plant grow freely for a year or two and watch how it flowers. You will then be able to assign it to a group." White Flower Farm has a detailed list of clematis species and their pruning requirements.

Group 1: flower in late fall/early winter on old wood. Prune after flowering by removing dead/damaged stems only. If a group 1 vine has outgrown its space, you can prune it to maintain a specific height. Just be sure to time the pruning right after it blooms, and be aware that there might be reduced flowering for one season. There are lots of varieties to choose from, including Clematis montana, which has white or pink flowers, some of which smell like vanilla, C. alpina, and C. macropetala, which have nodding bell-shaped flowers in various colors.

Group 2:  bloom in late spring/early summer. They can flower on new growth, but their larger flowers occur on older stems. Prune this group in early April by cutting off any dead or damaged stems. Trim the rest back to a strong bud, which will develop shoots from which flowers will grow in late spring. There is a vast array of Clematis patens hybrids and cultivars, including white 'Jackmanii Alba', 'Fair Rosamunde', which has pink flowers and often reblooms, 'Moonlight' with blooms white touched with a hint of yellow, and 'Ernest Markham' with large magenta flowers that was introduced in 1926.

Group 3: are the easiest clematis to grow and prune. These were some of the first clematis imported from Europe, and they are cold-tolerant to Zone 4. Many of these are cultivars of C. viticella, with deep purple blooms in mid-summer to fall on new growth. Plants are robust, reaching 9-20 feet tall. Some varieties are 'Etoile Violette', 'Betty Corning', 'Little Nell', 'Mme. Julia Correvon' and 'Polish Spirit.' Popular deep purple 'Jackmanii Superba' is included in this group as it is a hybrid between C. viticella and C. lanuginose. It is an improvement over the old standby 'Jackmanii'.

Another Group 3 clematis commonly found in local gardens is the late-blooming sweet autumn clematis, C. paniculata (syn. C. terniflora). Note that sweet autumn clematis can be invasive in our 6B climate zone. All Group 3 clematis are vigorous bloomers that flower on new growth and can be pruned as often and as hard as you like. Just cut them back to about 8 inches in early April.

There are shrubby clematis species, making them ideal for borders. For instance, Clematis integrifolia grows in a shrubby mound 12-24 inches tall with nodding, urn-shaped purple blooms. C. integrifolia 'Recta Purpurea' has purple foliage and small white flowers. Plants will require some support with stakes or a smaller garden structure. They fall into the Group 3 pruning class.

Clematis have been cultivated for centuries, providing versatility, beauty, and ease of care for gardens worldwide. With so many types to choose from, there is a place for clematis in every garden.

In addition to White Flower Farm, two specialty nurseries for clematis plants are: Brushwood Nursery and Hummingbird Farm.

Dianne Machesney is a Penn State Master Gardener. This volunteer program supports the outreach mission of Penn State Extension and provides research-based information on best practices in sustainable horticulture and environmental stewardship. For more information, contact the Penn State Extension of Allegheny County at alleghenymg@psu.edu or 412-482-3476.