Question about fertilizing container clematis

I could use a little advice about fertilizing my container clematises. I do use Osmocote, but I'm wondering if that's enough, or should I be using something more. Help me out here.

I use either Rose or Tomato fertilizer with Clematis regardless if they are growing in the garden or in containers. Since Clematis are heavy feeders, you should feed them in early Spring and AFTER they have bloomed.