Comtesse de Bouchard needs to be planted in full sun for profuse flowering. Since your CdB flowered well the previous years, I am wondering if a growing tree branch or similar growth from a nearby plant is shading your CdB. I had a similar situation. I ended up moving my CdB to a more sunny location.

Did you prune her down hard in the early spring?

Thank you both.

I do prune it down in the spring.

Since reading the comment about "planting in full sun", I've been racking my brain how this could apply because there has been no change in my plantings. Then as I was putting the garden to bed, I had an eureka moment. Both last year and this, I planted a nasturtium next to the Comtesse de Bouchaud. But this year the nasturtium went from being a trailing vine to an aggressive climbing vine, putting the clematis in the shade. So I'll be ultra careful about this next year.

P.S. A good many of my plants turned into giants this year (some of them unpleasantly so). I don't know if it was my new fertilizer (22-11-22) or if it was the weather.

Shade from the climbing nasturtium may have contributed, but the fertilizer may have as well. Fertilizers high in nitrogen (the first number in the N-P-K) and lower in phosphorus (the second number in the N-P-K) as yours was will grow leaves at the expense of flowers.

Is there a reason you are adding fertilizer? Have you had a soil test done? IME something slow-release such as compost is a better bet and will improve the soil tilth as well as adding nutrients at a rate the plants can absorb them.

Sorry. I expressed myself poorly. The fertilizer was used on the nasturtium which I believe transformed it from a trailing vine to a climbing vine. The nasturtium is not planted directly in the soil but sits in a pot on top of the soil next to this particular clematis.

Do you think the fertilizer leached through to the soil and thus to the clematis??? Normally I only use compost on all my clematis.

If you think it leached through then I'll forgo the fertilizer on the nasturtium and in this way perhaps, the nasturtium will go back to trailing instead of climbing which is what I want in this location.

Nitrogen moves very well through the soil. Whether enough came out of the potted nastursium to affect the clematis ???