Clematis are called the Queen of the Vines, and rightfully so. Their flowers possess a grace and elegance few plants can match.
A favorite perennial vine in gardens, this genus is available in dozens of species/cultivars that offer a variety of sizes, flower colors and bloom times. To get the best performance from clematis, consider its site and cultural needs and species-specific pruning.
Prepare a planting hole that is two to three times wider and several inches deeper than the root ball. Plant the top of the root ball 2-3 inches below soil level to encourage new roots along the stems. Backfill the hole with native soil enriched with organic matter (compost, leaf mold, etc.) and water well. During the first growing season, keep the plant pruned back to a height of 18 to 24 inches. This encourages both branching and the development of multiple stems from the buds underground. This initial training will maximize flowering and encourage the development of a healthy plant in the future.
Clematis has a specific set of requirements for maximum performance. Cultural considerations include light, soil, water, mulch, fertilization and structural support.
• For maximum flowering, the plant should receive five to six hours of sun daily.
• The soil should be organically rich, moist and well-drained.
• During dry periods, water well to keep the roots moist.
• Apply several inches of mulch around the base of the plant to keep the roots cool and moist. However, keep mulch away from the stems.
• Starting in early spring, fertilize with a balanced (nitrogen-phosphorus-potassium) organic fertilizer per the manufacturer's recommendations.
• Provide a structure on which the plant can grow, such as an arbor, trellis or mailbox post. For the more adventuresome gardener, clematis can be trained to grow on/through climbing roses, shrubs and small trees for interesting visual effects.
Pruning clematis does a number of things:
• Opens up the plant to air and light.
• Stimulates new growth.
• Encourages more flowering.
• Improves plant health.
• Controls the size of the vine.
Depending on the wood (old, new or both) that the plant blooms on and bloom time, clematis are divided into three groups -- A, B, C:
• Group A -- This group flowers on old (last year's) wood. These plants are the earliest to bloom, starting in spring. Because they bloom on the previous year's wood, pruning should be kept to a minimum, only removing dead stems. If additional pruning/cleanup is desired, wait until the plant finishes flowering. New growth will then have enough time to form flower buds for next year. Examples of this group are: Clematis alpina, C. macropetala, and their cultivars.
• Group B -- This group flowers on old (last year's) and new (current year's) wood. Stems from the prior growing season produce the heaviest flush of flowers in late spring, followed by a lighter bloom in late summer on new wood. In early spring, remove any dead stems. After the spring flowers fade, the stems that contained those flowers can be shortened. This group is the most challenging from a pruning standpoint, because the vines bloom on old and new wood. One may want to adjust timing of pruning/cleanup after observing the flowering during the course of a growing season. Examples of this group are: Clematis florida and its cultivars, 'Nelly Moser,' 'Niobe' and 'The President.'
• Group C -- This group flowers on new (current year's) wood, making it the simplest of the three pruning groups. These plants bloom in late summer or early fall. In early spring, cut back all stems to buds that are within 12 to 18 inches of the ground. Then let the plant do its thing for the growing season. Examples of this group are sweet autumn clematis (C. terniflora), 'Gipsy Queen,' 'Jackmanii' and 'Ville de Lyon.'
If an established clematis is pruned hard or at the wrong time, don't worry. It will survive. Most likely, the plant will flower at a different time than normal.
If you are unsure of the clematis species/cultivar that you have, observe its flowering habit over a growing season. After that, you should be able to assign a pruning group and adjust pruning and cleanup activities accordingly. The three pruning groups -- A, B, C are sometimes designated as 1, 2 and 3.
By taking the time to give clematis a good head start, providing it with proper growing conditions and knowing when to prune, you can enjoy the Queen of the Vines in your home landscape for many years.
Steve Piskor is a Penn State master gardener and Pennsylvania certified horticulturist. Columns by master gardeners sometimes appear in place of the Garden Q&A by Sandy Feather, a Penn State Extension educator.