Daylilies generally close at night. The majority of daylily flowers open in the morning and close by evening, completing their life cycle in a single day. The common name for these hardy perennial plants, scientifically known as Hemerocallis, reflects this fleeting, twenty-four-hour bloom period. While each individual flower is short-lived, daylilies produce many buds on a single stalk, or scape, ensuring a continuous display of color over several weeks.
The Diurnal Bloom Cycle
The standard behavior of a daylily flower is described as diurnal, meaning it opens during the day and fades as night approaches. This pattern is driven by the plant’s biological clock, which is sensitive to light and temperature cues. The flower opens rapidly over a few hours in the morning.
Once open, the flower is available for daytime pollinators, such as bees and butterflies, to transfer pollen. The flower undergoes programmed death, or senescence, typically within 24 hours of opening. This systematic closure and wilting of the petals and sepals conserves the plant’s energy and resources.
By quickly closing the spent flower, the plant focuses its metabolic energy on developing the seed capsule or maturing the next flower bud. This resource conservation helps the plant produce as many seeds and new blooms as possible. The closed flower also protects the pollen from exposure to wind, dew, and rain overnight.
The opening and closing involve changes in cell turgor and differential growth in the floral tissues. These rapid movements are a form of nyctinastic movement, responding to light and temperature changes. This specific life-span ensures a fresh bloom is available each morning, maximizing the plant’s reproductive efficiency.
Understanding the Name “Daylily”
The name “daylily” directly references the plant’s single-day bloom cycle. The scientific name, Hemerocallis, is derived from the ancient Greek words hēmera (“day”) and kallos (“beauty”). This confirms that the plant’s fleeting, one-day beauty has been a recognized characteristic for centuries.
Despite the common name, the daylily is not a true lily. True lilies belong to the genus Lilium and grow from bulbs, while daylilies grow from fibrous roots and a crown. Daylilies are classified in the family Asphodelaceae, which is botanically distinct from the lily family.
The misnomer is likely due to the visual similarity of the open flowers, which resemble a lily blossom. The name persists in common usage, but the defining feature of the daylily is the ephemeral nature of its individual blooms.
Exceptions to the Rule
While the diurnal pattern is the rule for most daylilies, specific breeding efforts have created varieties that defy the single-day closing time. These cultivated exceptions fall into two main categories: extended bloomers and nocturnal bloomers.
Extended Bloomers
Extended bloomers are cultivars whose individual flowers remain open for at least sixteen hours, stretching past the typical evening closure. Popular examples, such as ‘Stella d’Oro,’ open in the morning but stay fresh into the night. This extended duration means the flower is visible long after the sun has set.
Nocturnal Bloomers
Nocturnal daylilies represent a greater deviation, as their blossoms open late in the afternoon or early evening and remain open throughout the night. These night-blooming types, like Hemerocallis citrina, are often fragrant, attracting nocturnal pollinators such as moths. The flowers typically close the following morning or early afternoon, completing their cycle opposite to a standard daylily.