|When should I prune perennials, in the fall or spring, such as rebina and daylilies?|
|In general, you may trim away any browned and dead portions of perennials once frost has killed back the tops. On daylilies, as with many other perennials, this would certainly include old and dried up flowering stems. Evergreen crowns or foliage on perennials should be left as is over the winter, with any tidying done in the spring.
Some daylilies are evergreen and some semi-evergreen, on these plants the evergreen foliage should not be disturbed.
However, most daylilies are deciduous meaning their leaves turn brown and die off over the winter. Many gardeners will leave the collapsed and faded foliage in place over the winter as a natural protection for the crown, then remove all discolored foliage the following spring.
Other gardeners will remove any frost killed foliage in late fall and mulch around the crowns. Removal of the faded foliage in fall might be preferred if there have been pest or disease problems this past season, the intent being to reduce the chance of the problem wintering over and reoccurring next year.
Unfortunately I am not familiar with a plant called rebina, but the general guidelines of removing dead material as a matter of personal preference would most likely still apply.