I planted this clematis last spring & it didn't do very much over last summer. I didn't worry, I as I figured it needed to become more established. This spring, it was going gangbusters, and then about 3 weeks ago, just stopped. No new growth, the fledgling growth has stunted. The trees in the area have leafed out substantially. Could increased shade have caused this sudden halt? I've also planted a bleeding heart at the foot of the clematis. Could these two be poor companions? There is no sign of disease or pest damage. Thanks for all ideas/tips.