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The Homeowners Column
Clematis Pruning 101
State Master Gardener Coordinator
We're all ready to get outside and prune. Not just because plants may need it, but because it feels good. Spring pruning is winter catharsis. Hacking back a bunch of plants is a smack down to a winter we are all ready to forget.
The old adage is "you prune when your pruners are sharp". Many plants can be pruned in the spring. But wait! Take a deep breath and step away from the shears. If flowers are the goal, let's take a moment to determine how the plant on the chopping block grows. Does it produce flowers on old wood (last year's stems) or new wood (this season's new stems)?
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. Some plants are sort of pruning fool–proof such as 'Endless Summer' hydrangeas and reblooming roses. They bloom on new and old wood so no matter when you prune they still flower.
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 in spring just before the plant's active growth.
Now your eyes may be glazing at this point of old and new. Relax. Incorrectly pruned plants usually don't die from pruning mistakes. Worst case scenario - flowers are delayed until later in the season or until next year.
When to prune clematis is a bit of a mystery due to the many different types of clematis. Confusion also arises in early spring since all the stems look dead even when they are not. If you are new to pruning clematis, wait a couple weeks to prune when the buds start to show green growth so you can tell the dead from the living.
Clematis are placed in groups according to pruning needs and flowering periods. Designations vary depending on the author. Groups include: A, B, C or 1, 2, 3, or little pruning, half pruning or hard pruning.
Group 1 or A is the early flowering species that bloom in late April to late May and require little pruning. These flower on old wood. In spring remove only dead stems.
Group 1 includes: Clematis alpina 'Constance' and 'Pamela Jackman'; Clematis macropetala 'Lagoon'; and Clematis montana 'Elizabeth'.
Group 2 or B 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 flower on both old and new wood. Prune lightly in spring when buds begin to swell, removing dead and weak stems and reducing size if needed. The largest flowers will be produced on the old wood while new growth will provide bloom for late season. Group 2 can be pruned again immediately after flowering if needed.
Group 2 includes: 'The President'; 'Vino'; 'Anne-Louise'; 'Arctic Queen'; 'Bees Jubilee'; 'Crystal Fountain'; and 'Rosemoor'.
Group 3 or C clematis are the late large-flowered cultivars and other late blooming clematis species. These vigorous vines are easy to prune and require a hard annual prune. They bloom on new wood so it's hard to go wrong. Cut to a pair of healthy strong buds at the base of the plant in spring as the buds swell. If unpruned, flowers are produced at the top of a bony legged plant.
Group 3 includes: 'Comtesse de Bouchaud'; 'Rouge Cardinal'; 'Duchess of Albany'; C. tangutica; C. viticella cultivars such as 'Etoile Violette', 'Polish Spirit' and 'Madame Julia Correvon'; and some of the non-vining clematis such as Clematis durandii. The sweet smelling, late blooming Sweet Autumn clematis is also in this group.
Great resource is Chicago Botanic Garden's publication "Clematis for Northern Landscapes" http://www.chicagobotanic.org/research/plant_evaluation/index.php