The Tiger Lily (Lilium lancifolium) is a striking perennial known for its vigorous growth habit and ability to rapidly colonize new territory. Its robust nature and ability to rapidly expand a single planting into a dense clump often lead gardeners to seek methods of containment. The plant’s expansion is driven by highly effective, non-sexual reproduction strategies. This article examines the biological processes behind the Tiger Lily’s expansion and provides practical advice for managing its growth.
Reproduction Mechanisms Driving Expansion
The primary mechanism driving the rapid expansion of the Tiger Lily is asexual reproduction, resulting in the formation of genetically identical clones. This species is often a sterile triploid, meaning it rarely produces viable true seeds and relies on vegetative methods for propagation. The most effective method involves the production of small, dark, pea-sized structures known as aerial bulblets, or bulbils.
These bulbils develop in the leaf axils, where the leaf joins the main stem. As the growing season progresses, they mature and detach from the parent plant, falling onto the surrounding soil. Once on the ground, the bulbil acts as a miniature, pre-formed bulb ready to sprout roots and foliage, establishing a new plant nearby. A single mature stem can produce dozens of bulbils, allowing the Tiger Lily to quickly form dense colonies.
The second method of expansion occurs beneath the soil line through the division and proliferation of the underground bulb structure. The main bulb naturally produces small offsets, or bulblets, around its base. Over time, these offsets grow into independent daughter bulbs that remain clustered near the parent. This constant process of underground multiplication causes the original plant to become a thick, crowded clump.
Managing and Containing Growth
Controlling the Tiger Lily’s expansion requires intervention targeted at both the aerial and underground reproduction systems. The most direct approach to limiting its wider spread is the diligent removal of the aerial bulbils before they ripen and drop. Gardeners should inspect the leaf axils regularly, especially in mid to late summer, and gently pinch off the developing bulbils. Removing the spent flower stalks helps divert the plant’s energy away from bulbil production.
Managing the underground spread involves periodic digging and division to prevent overcrowding and maintain the health of the patch. Since the bulbs multiply to form dense clumps, they should be carefully dug up every two to three years, typically in the fall when the foliage has died back. The offsets can then be separated from the main bulb and either replanted with more space between them or completely removed from the garden area. If containment is necessary, installing a deep physical barrier, such as metal or plastic edging, can limit the lateral movement of the underground bulbs and offsets.
Potential for Disease Transmission
Beyond the physical containment challenges, the widespread presence of the Tiger Lily carries a significant biological risk for other ornamental lilies. Lilium lancifolium is a known asymptomatic carrier of the Lily Mosaic Virus (LMoV), a plant pathogen that can severely affect other lily species. While the Tiger Lily itself typically shows no or only very mild symptoms, its tissues harbor the virus.
This widespread presence poses a risk because the virus is easily transmitted from the Tiger Lily to susceptible hybrid lilies, such as Oriental or Asiatic varieties. Transmission occurs primarily through sap-feeding insects, specifically aphids, which pick up the virus while feeding and carry it to uninfected plants nearby. The resulting infection in susceptible hybrids causes symptoms like mottled, streaked, or distorted foliage and reduced flower quality. To mitigate this risk, it is recommended to isolate Tiger Lilies from other high-value lily cultivars, keeping them separated by a distance of at least several yards.