The genus Clematis includes some of the most popular and varied flowering vines grown in gardens worldwide. These vigorous, often woody climbers are prized for their spectacular, star-shaped flowers that can range in size from small bells to large, dinner-plate blooms. Achieving this abundant flowering, however, depends entirely on understanding the specific growth habits of the particular variety being cultivated.
Defining the Three Clematis Groups
The wide diversity within the Clematis genus necessitates a simple, practical classification system for gardeners. All species and cultivars are placed into one of three pruning groups, designated Group 1, Group 2, or Group 3. This categorization is based on two primary factors: the time of year the plant flowers and the age of the wood on which the blooms are produced. Understanding this system is the most important step in ensuring a healthy plant and prolific flowering. This grouping determines whether the vine flowers on old wood, new wood, or a combination of both.
Group 1: Early Bloomers Requiring Light Pruning
Group 1 clematis are characterized by their early spring bloom time, often featuring species like Clematis montana and C. alpina. These varieties produce flowers exclusively on “old wood,” which is the growth that matured during the previous year’s growing season. Pruning must be minimal because cutting back the vines significantly in winter or early spring would remove all the developing flower buds.
Any necessary pruning should be performed immediately after the plant has finished flowering in the late spring or early summer. This light pruning is generally limited to removing any dead, damaged, or tangled stems to maintain the plant’s shape and size. If an established plant becomes overgrown and tangled, a major rejuvenation cut can be performed, but this radical measure should not be repeated for at least three years.
Group 2: Large-Flowered Hybrids Requiring Moderate Pruning
Group 2 includes many of the popular large-flowered hybrid cultivars, such as ‘Nelly Moser’ and ‘The President’. These plants typically flower twice in a season, relying on a combination of old and new growth. The first, heavier flush of blooms occurs in late spring to early summer on the old wood from the previous year. A second, lighter flush of flowers appears later in the summer on the new growth that developed after the first bloom cycle.
Pruning for this group is done lightly in late winter or early spring before new growth begins. The goal is to remove dead or weak stems and trim back healthy stems to the highest pair of strong, visible buds. Heavy pruning at this stage is avoided because it would eliminate the buds responsible for the first, more spectacular display of flowers. A second, light pruning can be performed after the first flush of blooms has faded by trimming the flowered stems back by about one-third to encourage the second round of flowers.
Group 3: Late Bloomers Requiring Hard Pruning
Group 3 is composed of late-flowering species and hybrids, including Clematis jackmanii and C. viticella. These varieties bloom exclusively on “new wood,” meaning the flowers are produced only on the vigorous growth that develops during the current growing season. This characteristic makes a hard cutback not only safe but entirely necessary for robust flowering.
Pruning should be done in late winter or early spring, just before the plant breaks dormancy and new shoots begin to emerge. The vine must be cut back severely, reducing all stems down to a height of approximately 12 to 18 inches above the ground. This aggressive annual cut ensures that the plant channels all its energy into producing strong, new stems that will support the season’s abundant blooms.