Root competition damage -- after 6 years
I have four clematises under an arbor. I put them there 6 years ago and fronted them with dwarf deutzia Nikko. The combination was lovely, but last year I noticed I had fewer stems on the clematis and many fewer new green stems. I guess I lived in denial for a year, but now I need to get my clems healthy. The ones in question are Margaret Hunt, Etoile Violette, and Ascotiensis (Beata was planted there in the fall but didn't come up -- maybe not hardy?? -- but that's a different issue). Etoile Violette looks the worst. Ascotiensis is battling back the best and doesn't seem too bad.
There are three questions here, I guess:
1. Do you agree the deutzia is the likely culprit?
2. If I rip it out, what are replacement candidates (phlox subulata, dianthus, epimedium, tiarella??)
3. Should I rip all the clematises but Ascotiensis out, too, and start over? It's hard to imagine Etoile Violette putting forth enough stems to make a show for a long time. On the other hand, do the existing plants stand as good or better chance than new clematises?
I should mention that I have a half dozen other viticellas in other parts of the garden, and they're doing fine. Some of them have some root competition because they're growing up a tree or a shrub, but I guess I was more careful with my distances there. Also, I have dozens of integrifolias growing on shrubs and small tuteurs all over the place with never a thought to root competition, and they are all glorious.
But the arbor isn't. I have to change it. Input would be appreciated.