If you are fertilizing with organic slow release fertilizers, you won't affect your blooms. I have fertilized when things were budded up quite a bit and even blooming with an organic fertilizer and it doesn't seem to have affected them at all. What you don't want to do is hit them with a high nitrogen fast acting fertilizer as that might shorten the bloom time.

As to whethere you can guesstimate when something might bloom based on when they bloomed last year, the answer is sort of. What you can't factor in however is whether this year spring arrived earlier and how that might affect bloom time or how the plants being more established in the ground might affect their bloom time.

Nobody said this was easy! The good news in your message is that since I'm using Espoma Rose-Tone, I shouldn't have to worry if some of them start setting buds this week even though I fertilized a couple of days ago. The not-so-good news is that this isn't a science. I will never be able to reduce it to a spreadsheet that guarantees success. It's not that I didn't already know this, but I keep trying to nibble at the edges of predictability. Thanks for responding.

Not a problem. Just realize that when you finally think you have something figured out is when something happens that makes you wonder if you ever really knew anything at all! ;)

"Just realize that when you finally think you have something figured out is when something happens that makes you wonder if you ever really knew anything at all! ;)"

That has got to be one of the best statements in regards to clematis that I ever heard. :)