From a botanical perspective, the most fundamental difference lies in their plant structure. True Lilies (genus Lilium) grow from bulbs, which are modified underground stems with overlapping scales. These bulbs are perennial but lack a protective outer tunic, making them more susceptible to damage and desiccation. Their stems are singular and erect, producing leaves all along their length. In contrast, Daylilies (genus Hemerocallis) grow from a mass of thickened, fibrous roots and rhizomes known as a "crown." These storage organs are tough and allow the plant to survive in a wider range of conditions. Their leaves grow in a clumping, grass-like fashion directly from this crown, forming a fountain-shaped arching mound.
The foliage of these two plants is a key identifier. True Lilies possess leaves that are attached directly to the central stem, often in whorls or alternating patterns. Daylily leaves grow in a basal clump directly from the crown, with no central stem. The flower architecture is also distinct. True Lily flowers are complete and complex, with six tepals, prominent stamens holding large anthers, and a single central ovary. Each flower can last over a week. Daylily flowers, while also having six tepals, are borne on leafless, branching scapes that rise above the foliage clump. Their most notable trait is that each individual flower lasts only one day (hence the name), though a mature clump produces numerous buds for a long bloom period.
Both genera appreciate well-draining soil, but their needs diverge from there. True Lilies are particular about their "feet"; they require cool, moist, well-drained soil and often benefit from mulch or shallow-rooted ground cover to shade their root zone. They prefer full sun but their stems must be protected from scorching heat. Daylilies are exceptionally adaptable. They thrive in full sun to partial shade and are tolerant of a wider variety of soil types, including heavier clay, as long as drainage is adequate. They are notably drought-tolerant once established, though they perform best with consistent moisture. True Lilies are less forgiving of both drought and soggy conditions.
The nutritional demands differ due to their distinct storage organs. True Lilies are considered "heavy feeders," especially as they are preparing to bloom. They benefit from a balanced, slow-release fertilizer applied in early spring as growth emerges and again after flowering to help replenish the bulb for the next season. Daylilies are less demanding. An application of a balanced fertilizer or one slightly higher in phosphorus in early spring is usually sufficient to support their vigorous growth and prolific flowering. Over-fertilizing Daylilies, particularly with high nitrogen, can lead to excessive foliage at the expense of blooms.
After flowering, the plants have different energy storage strategies. For True Lilies, it is critical not to remove the foliage until it has yellowed and died back naturally. The leaves are photosynthesizing and sending energy down to recharge the bulb for the next year's growth. Deadheading spent flowers prevents energy waste on seed production. Daylilies are far less fussy. While deadheading improves appearance, it is not crucial for plant health. The foliage remains until killed by frost. Propagation also differs: True Lilies are propagated by scaling the bulbs or separating bulblets, while Daylilies are easily divided by cutting through the tough crown and separating the fan-like growths.
