Daylilies are sturdy plants that seldom have problems, but occasionally the leaves turn yellow due to improper care or disease. Planting daylilies in a well-drained soil, proper fertilization practices and good pest management helps prevent the conditions that cause yellowing leaves.
Too much nitrogen fertilizer may cause yellow daylily leaves and reduced flowering. Fertilize daylilies sparingly. Use 1 to 2 tablespoons of 0-20-20 or 5-20-20 fertilizer per plant in early spring.
Daylilies planted in soil that stays wet often develop fungal or bacterial diseases that cause crown rot. The plants often don’t recover from this condition. You may be able to save the plant by digging it up and removing damaged and dying parts of the crown and the leaves that are attached to them. Check the plant for insects and replant in an area with good drainage. Hot, humid conditions in the deep South also cause crown rot.
Yellow and brown streaks near the center of the leaves may be the result of leaf streak. This disease is caused by the fungus Aureobasidium microstictum, which sometimes responds to fungicides. Remove severely infected leaves and clean up leaves that fall around the plant, especially in fall. This disease, which overwinters in leaf debris, usually isn’t fatal but may be unsightly.