Have you considered phlox subulata? Soft pastel colors, relatively long bloom time and if it does get scraggly, you can mow it (high setting) and have it come back lush and green.

consider Bergenia:

or Pachysandra:

Until you remove the plastic you will need to keep a very close eye on the soil moisture for the clematis since it doesn’t allow moisture to percolate down into the soil. I would likely get some corrugated cardboard boxes from the grocery, appliance, or bicycle store and lay it out flat, and then cover it with mulch. This will keep down weeds, and when it comes time to plant, just pull aside the mulch, rip or cut the cardboard and fold under or remove the cardboard flaps, plant the groundcover, and then tuck mulch back in around it. Edge the bed to keep grass out.

I love Amsonia hubrichtii and have several plants of it in a mixed border that never has any extra moisture beyond rainfall, so it will do fine in the same moisture conditions as the clematis. I like the idea of contrasting foliage texture or color. Whether it would suit here depends on the look you want. In my central N.H. garden it is the size of a small shrub, about 3 1/2’ in all directions, fanning outward from a central point. Blue flowers about now for a week or two and the that lovely foliage texture all season. The fall color ranges from gold to a red-gold-orange mix some years.

Bergenia planted here looks awful from when snow melts until new foliage emerges so I don’t much like it, but that may not be an issue in your warmer area.

Some lower groundcovers with contrasting foliage color and/or texture that won’t bother the clematis in addition to the creeping phlox include:

Sedum Angelina

Veronica Georgia Blue

many of the rock garden Dianthus such as Firewitch

Iberis sempervirens aka perennial candytuft

flowering thyme

some of the sun tolerant spreading Heuchera aka coral bells

Apart from the scruffiness issues, the mock up with Bergenia is misleading in terms of scale. It makes it look as if the leaves are the same size as the Clematis flowers wheras they are far larger.

That is a seriously beautiful Clematis! I wouldn't plant pink near it, but something with white flowers and/or gray leaves to let it be the star and not clash.

i read the premise to mean the plastic will be removed AT planting.. and hopefully mulched ...

if i read it wrong.. remove it before planting .. and mulch properly ...

God [mother earth if you prefer] did not intend for plastic to be between the sky and the soil .. roots need air.. as much as water ... if not more ...

ken

Full sun is not a good exposure for pachysandra regardless of location. It is a plant that prefers shade or at least partial shade. And IME, bergenia is far too coarsely textured for this application. I'd consider any of the groundcovers suggested by NHBabs first.

No debate, I just don't share your opinion.

Thanks so much for all of your feedback!

You might consider Saponaria ocymoides. It's a spring bloomer with small pink flowers. It's also evergreen.