True lilies (Lilium) multiply naturally in the garden. They grow from a scaly, underground bulb structure that serves as the plant’s reproductive and storage organ. This multiplication is a form of asexual reproduction, producing new plants that are genetically identical clones of the parent. Understanding these mechanisms allows gardeners to manage and increase their stock effectively.
The Primary Method of Underground Multiplication
The most common way a true lily multiplies is through the development of offset bulbs, which are miniature versions of the main bulb. These offsets form underground, emerging from the basal plate of the mature parent bulb. Over several seasons, these daughter bulbs remain attached, drawing nutrients and energy from the established plant.
This continuous process of offset formation causes the lily to grow into a dense cluster over time. When a lily clump begins to produce fewer flowers or the stems become crowded, it signals successful multiplication. If left undisturbed, this natural division will eventually lead to overcrowding, which can reduce the vigor and flowering capacity of the entire clump.
Specialized Multiplication Through Stem Bulblets
A secondary multiplication method occurs in certain lily varieties, such as the Tiger Lily. These plants produce small, dark, pea-sized structures known as aerial bulbils, which develop in the leaf axils along the stem above the soil line. These bulbils are miniature, self-contained bulbs that detach from the parent plant when they mature.
Once the bulbils drop to the ground, they can root and grow into new, independent lilies. This process allows the plant to propagate itself over a wider area. Some lilies also produce tiny bulblets underground along the portion of the stem that extends below the soil, offering another layer of clonal reproduction.
Clarifying the Difference Between True Lilies and Look-Alikes
Many plants commonly called “lilies” are not true members of the Lilium genus, and their multiplication methods differ. True lilies multiply via their scaly, layered bulb structure and stem-based bulblets. Daylilies (Hemerocallis) spread using a crown of fibrous or tuberous roots that expand laterally.
Canna Lilies are tropical plants that spread through thick, horizontal underground stems called rhizomes. Canna multiplication involves the rhizome sending out side shoots that form new growth points. Similarly, the Peace Lily (Spathiphyllum) multiplies by crown division, where new shoots with their own root systems emerge from the central base, a structure distinct from a true lily’s layered bulb.
How to Encourage Division and Increase Stock
Gardeners can encourage multiplication by manually separating the offset bulbs from the main clump every three to five years. The best time for this intervention is during the plant’s dormant period, typically in the early autumn after the foliage has died back. Begin by gently lifting the entire clump from the soil, taking care not to damage the fragile roots or the scaly bulb structure.
Once lifted, carefully separate the small offset bulbs attached near the base of the parent bulb. Any bulblet the size of a large marble or larger has a good chance of developing into a mature plant. Replant these newly separated offsets immediately into fresh soil at the same depth as the original bulb. Providing optimal soil conditions and consistent moisture will help these new divisions establish a strong root system, eventually growing into flowering-size lilies within two to three seasons.