Lily of the Valley (Convallaria majalis) is a popular perennial ground cover cherished for its intensely fragrant, nodding white flowers that bloom in the spring. This plant forms dense, lush colonies, making it a favorite for shaded garden spots where few other plants thrive. To successfully cultivate or manage this vigorous species, it is necessary to understand the unique structure and shallow nature of its subterranean system.
The Anatomy of the Root System
Lily of the Valley does not possess a deep, single taproot; instead, its underground structure is dominated by rhizomes, which are modified horizontal stems that grow near the soil surface. These creeping rhizomes, often called “pips,” are the plant’s primary means of anchoring, storing energy, and vegetative reproduction. The bulk of this dense, mat-forming network is surprisingly shallow, typically residing just one to four inches below the ground.
The pips are pointed, bud-like structures that emerge from the rhizomes and push upward to form new leafy shoots. These rhizomes are thin and twisty, allowing them to spread rapidly and laterally in all directions to colonize new territory. This shallow, expansive growth pattern is what gives the plant its effective ground cover capabilities.
Proper Planting Depth and Technique
Successful establishment of Lily of the Valley directly depends on respecting the shallow nature of its rhizomes, or pips. When planting bare-root pips, they should be set into the soil with the pointed, growing tip just barely covered, generally about one to two inches deep. Planting them too deeply can inhibit their ability to sprout and establish properly.
Before planting, it is beneficial to soak the dormant pips in lukewarm water for about 30 minutes to rehydrate them. The soil should be loosened to a depth of at least 12 inches and amended with compost to ensure it is rich in organic matter and retains moisture well. Pips should be spaced approximately six to eight inches apart to allow room for the initial lateral spread. Consistent moisture is important until the plants are established, but good drainage is also necessary to prevent the shallow rhizomes from rotting.
Controlling Spread and Removal Strategies
The aggressive nature of the rhizome network means that Lily of the Valley can quickly overwhelm other garden plants if left unchecked. Because the rhizomes are shallow and run horizontally, the most effective physical control method is diligent digging to remove the entire network. This process requires using a garden fork or spade to lift the soil and meticulously sift through it to extract every piece of the creeping rhizome, as even small fragments can re-sprout.
For containing a planting area, a physical barrier is necessary to block the horizontal runners from escaping the designated space. Installing a seamless root barrier made of thick plastic or metal, buried at least 18 to 25 inches deep, can effectively slow the plant’s outward spread. For large-scale eradication, an organic approach involves smothering the area by covering it with a thick layer of cardboard or black plastic sheeting for an entire growing season. This technique works by blocking all sunlight, which starves the rhizomes of the energy needed for regrowth. Chemical options, such as a glyphosate-based herbicide, can also be applied directly to the foliage, though multiple applications are typically required for complete kill-off.
Safety Warnings Regarding Toxicity
Despite its delicate appearance and pleasant fragrance, Lily of the Valley is a highly poisonous plant, and all parts must be handled with caution. The leaves, flowers, red berries, and even the shallow rhizomes contain a concentration of toxic compounds known as cardiac glycosides. The primary toxin, convallatoxin, can interfere with the heart’s function, leading to symptoms like nausea, vomiting, and cardiac irregularities.
Ingestion of any part of the plant can be dangerous to humans and pets, with the berries posing a particular risk to small children. Even water from a vase holding cut flowers can absorb the toxic substances and become harmful if consumed. It is important to wear gloves when handling the plant during gardening tasks, and to ensure that all parts of the plant, especially the rhizomes removed during weeding, are disposed of safely away from animals.