I'd thin them, and maybe be aggressive about it. Was it overly wet in your area this year? I'd transplant them to a couple of different places in hopes of having them do well and recover from whatever is ailing them. And maybe put in some lighter, better draining soil where you did the thinning. Maureen

I thin mine when ever I see one not where I want them to be. You will not harm the ones left behind, if that is your concern. They are weed like in that you will never get rid of them now. They will reappear from the smallest bit of root left behind. It may take a year or two but they will return. You cannot be too aggressive in your thinning.