Lily of the Valley is a popular perennial plant, admired for its fragrant, bell-shaped flowers and its ability to form a dense groundcover. Its rapid and extensive spread is largely due to its distinct underground root system, which allows it to thrive and naturalize. Understanding this root system is key to appreciating its growth habits and managing its presence.
Lily of the Valley Root System Characteristics
Lily of the Valley (Convallaria majalis) possesses a rhizomatous root system, meaning it spreads through underground stems called rhizomes. These rhizomes are typically thin and root-like, rather than fleshy, with a creeping growth habit. They are whitish in color and form an interconnected network just beneath the soil surface.
The primary function of these rhizomes extends beyond simple anchorage. They serve as storage organs, accumulating water and energy reserves for the plant. This stored energy enables the plant to overwinter successfully and supports vigorous growth in the spring. Rhizomes are also central to the plant’s vegetative propagation, allowing it to quickly produce new shoots, known as pips, which emerge as new plants.
Root System Spread and Depth
The rhizomes of Lily of the Valley grow horizontally, allowing the plant to spread and establish dense colonies. These underground stems typically run just beneath the soil surface, sending up new shoots or “pips” every few inches. This horizontal expansion can be rapid, enabling a small patch to develop into a lush carpet of foliage.
While the rhizomes spread laterally, they generally remain relatively shallow, often planted with their growth buds only about 0.5 to 3 inches deep. This shallow depth, combined with their lateral growth, makes them effective as a groundcover. However, this spreading characteristic means Lily of the Valley can become invasive in many regions, outcompeting and displacing native plants if left unchecked.
Managing Lily of the Valley Root Growth
Managing Lily of the Valley’s rhizomatous root system is often a consideration for gardeners. One effective strategy involves installing physical barriers, such as edging or root barriers, around planting areas. These barriers should be buried at least 18 inches deep to contain the rhizomes. Growing the plant in containers is another containment method, which restricts its root growth within a defined space.
For established patches that need reduction or removal, digging is a common technique. It requires carefully digging down at least 10-12 inches to extract the rhizomes. Because even small pieces of rhizome can resprout, it is important to remove all fragments from the soil. Smothering the area with landscape fabric, cardboard, or several layers of newspaper covered with mulch can also suppress growth by blocking light and air, requiring at least one full growing season to be effective. Repeated vigilance is necessary to manage new sprouts as they emerge.