Pardon me for living sir. It's an oxygen problem in the root zone. I'd transplant it into a nursery pot that has many holes in the bottom. That will help the soil transpire. maybe add some perlite for more drainage and air. Look for the beginning signs of root rot. Brown, mushy, oozy, gooey, smelly, gluey, ect. If you have some good compost tea, dunk the cleaned roots in the tea to inoculate. Good luck, and Praise Baby Weed Jesus, let em live!