Climing clematis do not bloom?

I have some climbing clematis that are growing strong but have not bloomed for two years, any ideas why not?

Climing clematis do not bloom?
Clematis require full sun to grow best (6+ hours direct sun per day) though some dappled shade during the heat of the day is beneficial. Flowers of some red and blue large-flowered hybrids and the bicolors fade badly if they get too much sun (such as 'Nelly Moser,' 'Hagley Hybrid' and 'Hybrida Sieboldiana') and these should be planted in eastern exposures or partial shade. The site should be open enough to allow for air movement around the plants. Soil should be rich and well-draining with a pH close to neutral (7.0). Though the plant's stems and foliage should be in sun, the roots like a cool, moist environment. With the exception of C. montana, clematis do not compete well with large tree roots. Most clematis will require staking so the twining leaf petioles can cling and climb upward, though some gardeners choose to let the plants sprawl over the ground, over woodpiles, other plants, etc.





The main purpose in pruning is to help plants produce the maximum number of flowers. Annual pruning is recommended. Sometimes older, neglected plants can be cut back into older wood and new buds may break. Growth from old wood will likely be weak and slow, however. If no pruning were done at all, plants would still grow and flower profusely, though not where you may want them to. Some flowering would occur high in the plant and out of sight. Not all clematis can be pruned in the same way. There are three methods that can be applied to major groups depending on the time of year the plant flowers. No new growth must occur to enable the earliest flowering clematis to bloom, but the later flowering types must make new growth in order for flower buds to form. A few plants are not strictly bound to the following groups but may cross lines. Because vines will likely be entangled, make cuts carefully among the intertwining vines and spread and train them in various directions in order to cover the maximum possible area. This enables the plant to display its blooms rather than be bunched up.