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The Homeowners Column
Pruning Clematis Demystified
State Master Gardener Coordinator
Many of the questions that come in to the U of I Extension office start with "When do I prune (fill in the blank)". The answer to that question depends on how the plant grows and if it produces flowers on old or new wood. As a general rule plants that bloom before June 15 bloom on old wood and plants that bloom after June 15 bloom on new wood. For instance forsythia and lilacs bloom in early spring then as the season progresses the next years flower buds are produced on old stems. Pruning them now translates into no flowers next year.
For plants that bloom on old wood, it is best to prune right after they flower. For other plants, as a general rule, it is best to wait and do severe pruning just before the plant's active growth season. Therefore for summer blooming plants, prune in late February or early March when the severe part of winter has passed and spring is not too far away.
When to prune clematis seems to be a bit of a mystery, partly because there are many different types of clematis. In the 1950's a somewhat loose grouping was put together to help explain pruning and flowering periods.
At the recent Master Gardener State Conference in Lisle Illinois, Richard Hawke of the Chicago Botanic Garden outlined the groups. Mr. Hawke as director of the plant evaluations gardens also shared some of his favorite clematis.
Group 1 is the early flowering species which generally bloom in late April to late May. These include Clematis alpina 'Constance', Clematis alpina 'Pamela Jackman', Clematis macropetala 'Lagoon' (nice deep blue with double petals) and Clematis montana 'Elizabeth'. The Group 1 clematis bloom on last year's wood. These should be pruned after bloom, but only if necessary.
Group 2 clematis are early double and semi-double mid-season cultivars. They bloom mid to late May and if healthy will repeat bloom in September into October. These bloom on the new growth that is produced from old buds. If they are pruned to the ground, they will bloom but will miss the early flower period. These require minimal pruning to remove any dead stems in late March just as buds swell. These include 'The President' a nice rich purple or 'Vino' a deep red. 'Mrs. Cholmondeley' is light lavender blue and seems to tolerate more shade than other clematis.
Group 3 are the late large flowered cultivars and other clematis species. They flower in mid to late June into July. Clematis viticella cultivars are vigorous plants that bloom July through September. 'Madame Julia Correvon' is a rich red that blooms all summer. These bloom on new wood so you can't go wrong however you prune. Generally these should be cut to a living bud at about 18-24 inches from the ground in spring as the buds swell. If these are never pruned, the flowers are produced way up at the top of the plant leaving their skinny legs showing. Group 3 also includes some of the clematis that do not climb such as the indigo blue flowered Clematis 'Durandii'.
There is an amazing number of clematis now available from vigorous ones that can eat your house to delicate ramblers for the flower border. Choose the one just right for your needs and ones listed as resistant to clematis wilt. Plant two together to vary flowering times or to compliment colors. All you need is an area of at least half day sun where the roots can be kept moist and cool with a flagstone path, ground cover or mulch and with plenty of compost in the soil.
For more information on clematis, check out the book An Illustrated Encyclopedia of Clematis by Mary Toomey and Everett Leeds.