URBANA, Ill. – Some gardeners may make pruning mistakes in their haste to tidy up their gardens in the spring, according to a University of Illinois Extension horticulture educator.
“The old adage is ‘you prune when your pruners are sharp’,” says Sandy Mason. “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, take a moment to determine how the plant grows.”
The primary factor is whether the plant produces flowers on old wood (last year’s stems) or new wood (this season’s new stems). Mason explains, “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 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.
“Incorrectly pruned plants usually don’t die from pruning mistakes,” Mason reassures. “Worst case scenario, flowers are delayed until later in the season or until next year.”
Some plants are more foolproof, such as ‘Endless Summer’ hydrangeas and reblooming roses. They bloom on new and old wood; therefore, they should flower no matter when they are pruned.
Determining when to prune clematis plants can be a little more difficult, due to the many different types of clematis. Confusion also arises in early spring because all the stems appear to be dead.
“If you are new to pruning clematis, wait a couple weeks and prune when the buds start to show green growth, so you can tell the dead from the living,” Mason suggests.
Clematis cultivars 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 composed of the early flowering species that bloom from late April to late May and require little pruning. These flower on old wood. In spring, only the dead stems need to be removed.
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 in mid- to late May and, if healthy, will bloom again in September through 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 blooms for the late season. Group 2 can be pruned again immediately after flowering, if needed.
Group 2 includes hybrid cultivars ‘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 an unattractive and leggy plant.
Group 3 includes hybrids ‘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 and Clematis integrifolia. The sweet smelling, late blooming hybrid ‘Sweet Autumn’ is also in this group.
According to Mason, it is worth taking the time to do the homework on clematis to make the most of these attractive plants.
For more information, view the U of I Extension You Tube video entitled “Clematis Pruning Groups” as well as the many Extension gardening websites including “Vines: Climbers & Twiners” at http://extension.illinois.edu/vines/intro.cfm.