Ask-a-Dave's-Gardener: Dixie Wood Fern flopping, 1 by Redbudzzz

Redbudzzz wrote:
These ferns reached their full potential this spring, 4-5 feet tall fronds, upright, gorgeous in mostly shade. But just as they were finished unfurling, in mid-May, fronds started suddenly collapsing, one at a time. Not sagging outward they\'ve previously done over the course of the summer, just but falling flat on the ground in one day. I\'ve checked the stems and at first they just seem bent, after a few days they soften and become mushy/rotted. Any advice much appreciated!