Answer: Since your other plants are doing well, your general care must be fine. First you might check that this plant is not somehow located in a draft (hot or cold) or experiencing some other type of environmental stress. Next, it is possible that this plant could have been potted at a different time from the others and is in need of repotting; it might have overly crowded roots or be suffering from a build up of fertilizer salts in the soil. Check too that you are not overwatering, the soil should be moist but not sopping wet. However, I suspect there is a disease of some kind, possibly a root rot type problem, as these plants are somewhat prone to that. You might remove the pot and take a look at the roots, if they are not white and firm and healthy then the plant should be discarded. Otherwise, you might want to check with your local county extension and see if they can give you a more specific diagnosis. They might appreciate photos of the overall plant plus close-ups of the stems and foliage, possibly also a freshly collected sample enclosed in a plastic bag. I'm sorry I can't be more specific for you long distance.
Q&A Library Searching Tips