Just let them be is what I do! These are the most carefree plants in your garden, trust me.

Daisy,
If you want to tidy daylilies up, you can cut the leaves down to 6 inches height. Cut off the old leaves and flower stalks of iris to prevent soft rot and overwintering iris borer eggs. Keep the dirt off the top of the iris rhizomes so that the sun can hit them. otherwise, they don't bloom as well.

Its not necessary to mulch established plantings of daylilies, and certainly don't do it to the iris for the above reasons.
Renee