Remove the suffocating plastic and replace with cobbles or organic mulch. Bald on the inside but with leaves beyond may have been due in this case to wet conditions for a particular period. Such as from heavy summer rains typical of your region. Renewal pruning (cutting down to short stem lengths) to start over with fresh tops should be done at end of winter.

agree.. completely remove the plastic ...

if you arent starving them for water.. you might be baking them due to retained heat ....

what is the red stuff on top of it .. almost looks like plaster???

its real STRESSED .. it is not hungry.. fert is not an option ...

ken

The red stuff is old mulch we're about to redo. The plastic is actually not covering the plant; there's an opening about 2.5 ft in diameter to let the soil get water/air. We use the plastic around the plants and under the mulch to keep weeds out. Some of the black shown in the back are actually the tabs on the edging between the mulch and the rocks.

I have other plants (loropetalum, Indian hawthorn) in the same area and they're all doing fine. If it's the plastic that's the problem, it's peculiar the abelia are the only plants affected. We've planted other things in the flowerbed the last 15 years--plastic & all--never an issue. If it's that stressed, maybe I'll dig it up and pot it.

Chop it!

We know the plastic isn't covering the plant but it is covering the soil around the plant. That isn't conducive to plant health. It doesn't keep weeds down in the long run, they just grow on top of it then through it and it creates a nightmare problem for anyone trying to cultivate the bed in the future.