Daylilies (Hemerocallis) are one of the easiest flowers to grow and rarely have problems, according to the American Hemerocallis Society. In general, daylilies are planted once, then put on a summer display of beautiful blooms every year. If you begin to notice a problem with your daylilies, such as they’re not blooming as they once did or they are being eaten up by bugs, take care of the issue right away. The problem will only get worse over time and will become more difficult to solve.
Divide daylilies in the fall after they die back if they become overcrowded and are producing smaller and fewer blooms. Dig up the rhizomes, cut them so each section has an eye and replant. Division typically needs to be done every four to five years.
Avoid cutting off the foliage until after it dies in the fall. Daylilies photosynthesize the sunlight into energy. If the foliage is cut too soon, your daylilies will not thrive.
Apply insecticidal soap and spray down the leaves to control pests, such as aphids, spider mites and thrips. Alternatively, lay out a blue piece of cardboard with some petroleum jelly smeared on it to trap thrips. Do not attempt to get rid of beneficial insects, such as green lacewings and ladybugs, which kill the harmful insects. For snails and slugs, remove the mulch where they hide.
Remove daylilies from your garden that are afflicted with the leaf streak. Leaf streak, caused by the fungus Collecephalus hemerocalli, is indicated by brown spots or streaks starting at the tip of the leaves and leading to with yellow edges.
Stop watering your daylilies if they begin to rot near the stem. Throw out the infected plants before the rot spreads. Too much water causes the bacteria Erwinia carotovora. Dig up your healthy plants and replant in an area with better water drainage or mix in some compost or another organic matter to improve drainage.