Clematis vines are capable of producing at least 100 large, colorful blossoms each year and grow between 2 and 30 feet long depending on cultivar and conditions. Clematis are divided into three main types based on when they bloom, and each type has its own guidelines on when it is best to cut them back. To determine when you should cut back your flowers, watch them to find out when they bloom and prune accordingly.
Clematis are made up of woody, deciduous vines that vary in size and spread. Some of the more vigorous varieties grow as much as 20 to 30 feet, while those with larger blooms only reach 8 to 12 feet long. The smaller species grow to only 2 to 5 feet tall. Clematis flowers start off slow and then by the third year they begin growing much faster. Clematis vines produce blooms in a variety of colors; such as white, blue, violet, pink, red and multicolored. Clematis may bloom in spring, early summer or fall.
Early-season clematis flowers bloom in the spring, during April and May. They produce their flower buds during the autumn months, which stay attached in the winter. Only trim shoots that bloomed flowers this season after the plant has finished its bloom cycle. Do not prune this type of clematis after July, in order to give it plenty of time to recover before it begins budding for the next season's growth. Prune back vines at this time only to control and shape the plant, but avoid pruning into the main vines of the trunk.
The large-flowered varieties bloom in mid-June on the previous season's growth. They also are capable of producing a second set of blossoms later in the summer on the newer growth. Remove only weakened or already dead shoots during later winter and early spring. Keep those with the largest or the strongest buds for the new season's blooms. Deadhead these blossoms to encourage a new set of blooms. At this time you can cut back the plant to 12 to 18 inches; however, doing so could cause the second set of blossoms to appear smaller.
Some varieties of late-blooming clematis begin to flower as early as mid-June, but they continue to bloom throughout the summer and into the fall. They are the only clematis type that produces blossoms solely on the current season's growth. In the early spring, cut back the whole plant to 24 to 36 inches and remove all dead growth.