Three reasons an established clematis may fail to bloom include:
1. Not enough sun. Clematis tolerate and even benefit from a little shade but too much shade leads to few or no flowers.
2. Too much nitrogen. A lot of nitrogen can lead to abundant foliage with few or no flowers. (Be sure lawn fertilizer isn't applied near the vine.)
3. Improper pruning. Some clematis bloom only on old wood. If these varieties die back in winter or are pruned heavily in spring, they won't bloom because little or no old wood remains. Clematis are divided into three pruning categories. Check the following information to learn how to grow clematis and prune them properly: Growing Clematis and Clematis: Pruning.
