Clematis are beautiful, versatile vines, often referred to as the queen of flowering vines. There are more than 250 species of clematis with several hundred cultivars. Not all of these will grow in Iowa, but many are hardy here. Clematis offer a wide range of colors, double or single flowers, with different flower forms, blooming from May until October. Clematis growth also is varied. Some vines grow only a few feet in a season, while others grow up to 12 feet.
How to prune a clematis is a common question for Master Gardeners.
There are essentially three types of clematis.
•Type 1: Blooms on the previous season’s growth or “old wood.” This group is the trickiest to grow in Iowa because a winter like last winter can cause severe winter dieback, resulting in few, if any, flowers. If this is the vine you have, you can encourage more blooms by removing the vine from its support in fall, laying them on the ground, and covering them with several inches of mulch. After spring bud break, prune the vine back to live wood.
•Type 2: Flowers on old and new growth. These vines usually are repeat bloomers, with two blooming periods showing off large flowers in early summer that are produced from last year’s growth and then a rebloom in late summer on the current year’s growth. This vine might produce fewer blooms in the spring if winter dieback was extensive.
•Type 3: Flowers on new growth. These vines produce one large bloom flush during the season produced by the current year’s growth. This is the most reliable bloomer in Iowa. These vines can be pruned to 6 to 12 inches off the ground in early spring. I follow an alternative pruning method, waiting until bud break in spring and pruning back to the uppermost new growth.
Clematis thrive in rich, well-drained soils and require at least six hours of sunlight each day to perform well. Mulch is a must, providing winter protection for the crown and it helps to keep the root system cool during summer heat.
Clematis vines need support from a trellis, fence, deck railing or other structure. Not many pests attack clematis but they are affected by “clematis wilt” where part of the vine suddenly will wilt and die.
It rarely kills an entire plant. For wilt, simply cut back the dead vine at ground level and remove it. The plant usually will send up new shoots.
For more information about clematis and a list of varieties that grow well in Iowa, visit Iowa State Extension at Store.extension.iastate.edu/Product/rg307-pdf. You can also call the Linn County Master Gardener hortline at (319) 447-0647.
•Lisa Slattery is a Linn County Master Gardener.