another pic.
kurt

Is this star jasmine (Trachelospermum jasminoides)?
If so the leaves might be turning red due to the season or perhaps too much sun or a root issue (too much water, not enough oxygen for the roots, etc.).
I did a search for Trachelospermum jasminoides red leaves and came up with several hits.

Good luck!

-Robert

Here is a link that might be useful: One search result

Hi Robert. Thanks for the reply. That thread is helpful. Perhaps the color and the relative lack of leaves are indeed partly or entirely seasonal. But here are a few more details, partly in response to things you mention, partly just FYI, in case they spur any other particular thoughts:
-- They're only getting about two hours of sun a day.
-- I've been watering them thoroughly once a week, more if it's hot and the top inch or so of soil starts feeling dry.
-- They are in terra-cotta pots with nothing containing water that drains through.
Kurt

Perhaps the color and the relative lack of leaves are indeed partly or entirely seasonal

Unfortunately not. This vine is fully evergreen in areas where it is hardy. Even here in my borderline zone, it remains full and green through fall or in cold weather. The colored foliage and the leaf drop is indicative of something not right with its growing conditions - poor quality potting soil/drainage, too little water, lack of nutrients. Check to see if any of these may be an issue, but evergreen vines that look like that now usually mean they are on their way out..........sorry.

Robert:⦠And yes I believe they are star jasmine.
Gardengal48: thanks for the hard truth. As for the possibility of too little water, I feel like I'm giving them enough, but they do look like they need water. perhaps it's not penetrating well. Maybe next watering I'll try poking some holes.