This Clematis belongs to the third group of Clematis - a group including Clematis which flower in late summer on growth made in that season. It is also poisonous for humans, according to North Carolina State University. Climbing to a modest 4’, Nubia packs a punch with large 5-6” crimson star-shaped blossoms accented by purple anthers. They should be pruned in late winter or early spring and require 'hard pruning': simply cut back the stems to a pair of strong buds about 1ft. Prolifically flowering, the sumptuous show goes on from late spring through summer, repeating in autumn. This Clematis belongs to the second group of Clematis - a group including Clematis which flower in early summer on short shoots developing from the last year's growth. Pruning Clematis 'The President,' Its Relations With Animal Life . How to grow Group 1 clematis. If the label on your clematis doesn’t have class information or you just aren’t sure which class your clematis belongs to it’s easy to determine, just go by bloom times. Group 1 clematis to grow. This vine is a group 2 type when it comes to a pruning regimen. Group 1 clematis. These Clematis vines should be pruned in late winter or early spring before new growth starts and after the first flush of flowers in early summer. (30 cm) above ground level before growth begins in early spring. Stems that bloom late should be hard pruned, about a foot from the ground. There are three categories of clematis – group 1, 2 or 3 – which require pruning at different times. Pruning this group takes a bit of finesse but can be done if you pay attention to blooming times throughout the season. Stems that bloom early should be dead-headed after the flowers fade, but not cut back, as they will produce buds for the following season. This group doesn’t need pruning, but you can remove old or damaged stems after they have finished flowering, if needs be. The ASPCA lists clematis as being toxic to dogs and cats. This means that you should prune it right after the first flowering. It is best to prune it every other year. Group 2 clematis. Some flower again in late summer on new growth. Pruning group 2. These early-flowering clematis burst into bloom in winter and spring on the previous year’s growth.