Pruning Clematis. When they bloom determines when to prune. Related articles: 1. "The Many Faces of Clematis. Get to know the wide variety of flower shapes and sizes this popular vine offers." 2. "Clematis with Everything. An avid collector uses shrubs and perennials as living trellises for these flowering vines." 3. "Three Myths about Clematis. Think you know clematis? Think again."