I've read on this forum that fertilizing clematis while they are blooming shortens the length of the bloom. I can't say whether this is true or not because I always fertilize when I cut them back in the Spring.

I meant to say that I can't say from my experience. I do not question that it may be true.

Wouldn't it depend somewhat on the type of fertilizer you were using? I use slow release fertilizer and have never had a problem. Just a thought.

You should not fertilize your clematis once buds have come out or they will all flop out. I learned that last year. I was wondering why all the blooms of my clematis are flopping out until I stumbled upon an article from the garden section of our newspaper that said, fertilizing clematis when already in bloom will cause the flowers to flop.