Possibly too much nitrogen. That would cause them to have all greenery and no blooms. Some plants will bloom better if you cause them a little grief, like letting them dry out every now and then and withhold the high nitorgen fertilizer. Try just using compost.

The clematis can be pruned to the ground in winter if it doesn't die back naturally. It should bloom early in the season and then rebloom off and on during the summer. It should also be larger and more "bloomiferous" every year. I don't actually use any kind of fertilizer on mine other than compost, they get plenty of nutrients just from the soil. Cheryl

My snaps were doing the same thing ..they were short on sun..I cut some tree branches down and now they are loaded with blooms..I guess 3-4 hrs a day will do it ...

Good Luck
jake