Daylilies (Hemerocallis) are a highly popular and resilient group of perennial plants known for their striking, short-lived flowers and durability in various landscapes. Gardeners often seek to understand the daylily’s underground structure, which allows it to survive harsh conditions and regrow reliably year after year. This structure is frequently, but mistakenly, referred to as a “daylily bulb” due to its ability to store energy and moisture. To properly plant and care for these perennials, it is helpful to know what the underground growth actually looks like and how it functions.
Understanding the Daylily Root System
The daylily’s underground growth is not a true bulb. Instead, this herbaceous perennial grows from a specialized structure known as a crown and an accompanying mass of fleshy roots. The entire underground system is often described botanically as fibrous-tuberous. This system acts as the plant’s pantry, storing the water and carbohydrates necessary for survival and vigorous spring growth.
The roots and crown enable the plant to endure periods of drought and cold dormancy, making the daylily a highly resilient plant. When a daylily is dug up, the entire clump of roots and the central growth point must be present to successfully start a new plant. This contrasts sharply with true bulbs, which are self-contained storage organs that regenerate on their own.
The Physical Appearance of the Crown and Fleshy Roots
The daylily structure is a distinct unit composed of the crown and two types of roots. The crown is the solid, knot-like core where the leaves and roots meet, typically appearing white or pale green. This small, dense section is the plant’s central growing point and must remain intact for the plant to thrive. All new foliage and flowering stems emerge upward from the crown.
Extending downward from the central crown are the fleshy storage roots. These roots are thick, light tan or cream-colored, and are cylindrical or spindle-shaped, resembling thick fingers or a cluster of small sweet potatoes. They can be quite brittle and easily snapped if handled roughly. A mature daylily clump can form a dense, heavy mass of these roots, often a foot or more in diameter.
Interspersed among the thick, fleshy roots are the finer, darker, hair-like feeder roots. These smaller, more delicate structures are responsible for the immediate uptake of water and minerals from the soil. The fibrous feeder roots are the plant’s active drinking system, complementing the long-term storage of the fleshy roots. When purchasing a bare-root daylily, a healthy specimen will have a firm crown and a substantial network of these fleshy and fibrous roots.
Distinguishing Daylily Structures from True Bulbs and Tubers
The daylily’s structure is botanically classified as a tuberous root, which is a modified root for storage, unlike a true bulb or a true tuber. A true bulb, such as a tulip or onion, is a modified stem enclosed by fleshy, layered scales and often covered by a papery outer skin called a tunic. If sliced in half, a true bulb reveals these concentric layers and a miniature, embryonic flower inside. True tubers, like a potato, are modified stems that are solid and lack the layered structure of a bulb. A tuber has multiple growth points, commonly called “eyes,” from which new plants can sprout.
In contrast, the daylily’s tuberous roots must be attached to a piece of the crown to produce new foliage. This distinction is important for planting: true bulbs are planted deep, two to four times their height, to allow the stem to elongate. Daylilies, however, must be planted with the crown barely below or right at the soil surface to prevent rotting.