There appear to be marestails sprouting around the plant. So I'd kill two birds with one stone. Dig up the affected plant and examine the roots for dryness, rot, pests or voids in the soil beneath it. Meanwhile try to eradicate the marestails. They will be a pain for ever if left alone.

@floral: good eye, it’s horsetail that you spotted and it has taken over my garden beds. My strategy to deal with it is to add plants that will hide it and outcompete it. Rozanne is great for that purpose!

It’s strange, the sick-looking plant is not the only one in my garden doing that. Could it be some type of fungus, insect or bacteria? Or maybe too much sun?

Thanks!

I had one that looked similar a few years ago, with many red splotches...it was right next to a sprinkler head, so I surmised it was receiving too much water. Could that be the issue with yours?

@lovemycorgi: thank you but I don’t think so. I watered only once this year since we’ve been having regular rain.

I see some new, small green leaves, which to me says this plant is healthy. You could snip off the leaves that look the worst, otherwise I would leave it alone and see what happens. I have no idea what caused only one plant to do this.

Mine did that once when it was getting to much shade it started getting its fall colors early...