I have 4 phormiums of different varieties. 2 are four years old, 2 were planted last Spring. All have or are in the process of collapsing -- all the leaves are lying flat on the ground. On the 2 newest and smallest ones, the leaves have detached from the plant. I am sure these plants are goners, but wonder what the problem was. I hesitate to replace them if new ones will also die.

Any advice would be appreciated. If this question belongs on a different forum, please advise.

Thanks.