Experts and BHG readers answer.
Why did my daylilies develop crown rot? What should I do this year to keep this from reoccurring?
Daylilies are hardy through Zone 3. Unless you live in a colder zone, it's not necessary to cover them with winter mulch to the extent that you did. Heavy winter mulch traps moisture and encourages rot. You could put bark mulch around the plants, but avoid covering them with anything that will prevent good air circulation.