Help with Clematis, Please (grown, fertilizer, concrete, backyard)

[Lodestar]

I have two "Jackmanii" in my yard. The south-facing one grows in a bit of a low spot and probably gets too much moisture but it grows and blooms like crazy. Of course, no one sees it but a neighbor and us.

The other faces West but is on the east side of the house. Gets enough sun to grow, though. Everyone can see my poor, abused child from the street. Yikes.

It did fine for several years then started to die back. The leaves turn yellow early and there are few blooms, mostly at the ends.

I tried a fertilizer for clematis last year but have the same problem this year. I've added a little bone meal to the soil and sprayed the leaves with Neem oil and am waiting to see if this makes a difference. I see no evidence of parasites.

This plant has two phlox planted at its base and several years their leaves have yellowed also. The neighbor's house and ours both have stone foundations and I've wondered if that may be leaking into the soil. I tested the soil but not sure if I did it correctly.

Any suggestions about what may be wrong?

[twinkletwinkle22]

Clematis leaves like sun but it's roots need protection from sun or the plant will not be happy.
Your home's foundation (concrete probably) could definitely be harming the roots, the phlox is giving you clues.
Why not move them to another spot and see if they will grow better.

I've grown clematis in past and they were picky about location.
Currently have a biggish clematis in a pot, blooming done for now, and I'm trying to decide where to plant it.
Neighbors (multiple of them) have clematis at their mailbox but I don't want my mailperson to contend with bees.
Will probably put mine in south-facing sunny backyard and mulch roots well.

[webster]

They respond well to hard pruning. But sometimes the plant is just from bad stock and replacement might be necessary from a different nursery if the pruning doesn't help.

[Lodestar]

The foundations are stone - pre-cement. In this area I believe there would have been a lot of limestone in the material.

But the clematis is on a fence at the yard's boundary so maybe twenty feet from our house and a good six feet from neighbor's house. Nonetheless, along that side of our house the impatiens used to get enormously high and then, after years wouldn't grow there at all. Something not right, but I'm mystified.

I could try cutting it back for this year. It leaved out at the bottom and then nothing until the very top. Poor thing.

When should it be pruned? Wait until Spring?

[Lodestar]

I've read up on pruning and think that is the next thing I will try. Can't remember how long that plant has been with us. Perhaps it needs a new start? I'll wait until fall.

It that hasn't helped I'll need to think about a new spot for it. Even though the phlox bushes shade its roots I'm wondering if it isn't just too hot there in the afternoon. My south-facing one gets a little shade from the sumac during the hottest part of the afternoon.