The daylily's journey into American horticulture begins not with a single event, but with the arrival of two primary species: Hemerocallis fulva and Hemerocallis lilioasphodelus (formerly H. flava). These plants, native to Asia, were brought to Europe by traders and explorers and subsequently crossed the Atlantic with early settlers. H. fulva, the common tawny or orange daylily, is a vigorous, tetraploid species that naturalized with remarkable ease along roadsides and in old homesteads, earning it the nickname "ditch lily." Its success is a direct result of its plant biology: it propagates aggressively through stolons and rhizomes, forming large clumps that crowd out competitors. H. lilioasphodelus, the lemon lily, is a smaller, diploid species valued for its fragrant, yellow flowers. These two species represented the genetic foundation upon which American hybridizers would later build.
The initial popularity of daylilies in American gardens can be attributed to their undeniable horticultural virtues, all inherent to their physiology. First and foremost is their legendary hardiness and adaptability. Daylilies are herbaceous perennials with thick, fibrous or tuberous roots that allow them to store water and nutrients, enabling survival in a wide range of climates and soil conditions, from USDA zone 3 to zone 9. They are not true lilies (Liliaceae) but belong to the Asphodelaceae family, which partly explains their resistance to diseases like the lily-specific viruses. Secondly, their growth habit is low-maintenance. They form dense clumps of arching, linear foliage that suppresses weeds, and they require minimal care once established. The common name "daylily" itself refers to the ephemeral nature of each individual flower (anthesis), which typically lasts only one day. However, each flower scape (stalk) produces a prolific succession of buds (a trait called prolification), ensuring a display that can last for weeks.
The true explosion in daylily popularity began in the early 20th century, driven largely by the work of American plant breeders like Dr. Arlow Burdette Stout. His work at the New York Botanical Garden from the 1920s to the 1950s was groundbreaking from a botanical perspective. Stout applied rigorous scientific principles to hybridization, focusing on fertility and expanding the plant's genetic diversity. He discovered that the common H. fulva was a sterile triploid, but by using fertile species like the yellow H. lilioasphodelus and others, he was able to create new, fertile hybrids. This work unlocked a world of possibilities. Hybridizers began manipulating ploidy (the number of chromosome sets), leading to the development of both diploid and tetraploid cultivars. Tetraploids, with their larger cells and thicker, sturdier flower parts, offered a new canvas for form and color.
Today's daylily is a testament to the power of selective breeding to transform a plant's characteristics. Modern hybridizing has moved far beyond the simple orange and yellow species. The focus is now on altering nearly every aspect of the plant's morphology. Flower form has been diversified into types like circular, triangular, spider, and double. Petal substance and texture have been enhanced for better weather resistance and a sparkling or velvety appearance. The color palette has been expanded to include every hue except pure white and pure blue, with patterns like eyes, edges, and watermarks adding complexity. Beyond the flower, plant habit has been refined, with breeders selecting for shorter, more compact scapes for landscape use or taller, more branched scapes for dramatic effect. Reblooming genes have been intensely selected for, creating cultivars that flower repeatedly throughout the growing season, overcoming the limitation of the single-day bloom. This continuous genetic innovation ensures the daylily's enduring status as a cornerstone of American horticulture.
