3. Once planted, gently tamp down the soil to eliminate air pockets. Keep the clematis well watered and avoid synthetic chemical fertilizers during the first year to allow the plant to adjust naturally to garden conditions. (The compost or manure added to the bottom of the hole will supply all the nutrients the plant needs for the first year.) Train young vines to climb trellises and other structures with garden ties, which can be discarded once the clematis becomes established after the second year.
Clematis vines are divided into three groups according to their pruning requirements. As a general rule, those in Group 1 flower on old wood, Group 2 on both old and new wood, and Group 3 on new wood. If you’re not sure which category your clematis belongs to, look for the remnants of last season’s blooms—if they are on the youngest, thinnest stems, the plant sets flowers on new growth; if they appear on thick, woody stems, it blooms on old growth. (See chart, below, for specific pruning instructions.) That said, many gardeners bend the rules to suit their preferences, pruning before buds set to delay flowering or to control plant height.
Regardless of which group your vine belongs to, all clematis require a hard pruning (to 30 to 40 centimetres from the ground) the first spring after planting to encourage new growth to emerge from the base.
Pruning: Simple as 1-2-3
Group 1: Evergreen and early-flowering types such as Clematis alpina, C. macropetala and C. montana and their cultivars Zones 6 and 7
Blooming habit: On old wood
Second spring: Cut back all stems to 1 m from the ground immediately after flowering
Subsequent years: After flowering, remove dead or weak stems; rejuvenate robust C. montana cultivars every third year by cutting all stems to 50 cm above the ground
Group 2: Early- and midsummer-blooming, large-flowered cultivars, including Jackmanii hybrids and double and semi-double cultivars; most clematis grown in Canada belong to Group 2 Zone 4
Blooming habit: First flowers appear on old wood; second flush on new wood
Second spring: In late winter or early spring, cut back all stems to at least 1 m from the ground
Subsequent years: Prune in late winter to a strong pair of buds 50 cm to 1 m from the ground; if extra height is desired, remove only weak or dead stems
Group 3: Late-summer-blooming, large-flowered cultivars; viticella types and late-flowering species such as texensis Zones 5 and 6
Blooming habit: On new wood
Second spring: In late winter or early spring, cut back all stems to 50 cm from the ground
Subsequent years: Same as in second spring, but cut back stems to 50 to 75 cm from the ground; remove weak or dead stems