Common Lily of the Valley Problems and How to Solve Them

Lily of the valley, or Convallaria majalis, is a woodland plant known for its delicate, bell-shaped flowers and sweet fragrance. Many gardeners appreciate its ability to thrive in shady areas where other plants might struggle. However, this plant can introduce a unique set of difficulties for homeowners and garden enthusiasts. Understanding these potential issues is part of responsibly managing this perennial.

Invasive Growth and Spread

One of the most notable characteristics of lily of the valley is its tendency to spread aggressively. The plant propagates through a network of underground stems called rhizomes, which extend horizontally. This system allows the plant to form dense colonies that can overwhelm neighboring flora and other garden ornamentals, quickly transforming a spot into a monoculture.

To manage this vigorous growth, containment is a primary strategy. Planting lily of the valley within physical root barriers can restrict the spread of its rhizomes. These barriers should be sunk at least 18 to 24 inches into the ground to be effective. Alternatively, growing the plant in containers keeps it entirely confined, offering a simple way to enjoy its blooms without it taking over the garden.

For patches that have already become unruly, removal requires diligent effort. The most effective method is to dig up the entire area, carefully removing all rhizome fragments from the soil, as even a small piece can resprout. After digging, covering the area with cardboard or a tarp for a full growing season can help smother any remaining rhizomes. Repeated efforts may be necessary to fully eradicate an established colony.

Common Diseases

While generally hardy, lily of the valley is susceptible to fungal diseases, particularly in damp, humid conditions with poor air circulation. Leaf spot is a common ailment, appearing as small, round, brown spots with purplish-brown borders on the foliage. These spots can weaken the plant and, in severe cases, cause leaves to wither, which can reduce the following year’s flower production.

Another frequent fungal issue is rust. This disease manifests as yellow patches on the upper surfaces of leaves, with corresponding brownish-orange, powdery pustules on the undersides. These pustules contain spores that can easily spread to other plants when foliage is wet. Like leaf spot, rust can diminish the plant’s overall vigor.

Managing these diseases involves cultural practices that promote a healthier growing environment.

• Improve air circulation by thinning overcrowded patches.
• Water plants at the base, directly onto the soil, to keep the foliage dry and discourage fungal spore development.
• Promptly remove and dispose of any infected leaves as they appear to prevent the spread of the disease.
• Conduct a thorough cleanup of all plant debris in the fall to reduce fungal material that can survive the winter.

Pest Infestations

Due to its toxicity, lily of the valley is resistant to many pests, including deer and rodents. However, a few invertebrates can cause noticeable damage to the foliage. The most common culprits are slugs and snails, which thrive in the same moist, shaded conditions that the plant prefers. These gastropods chew irregular holes in the leaves, leaving behind slime trails.

While this damage is mostly cosmetic and rarely fatal, it can detract from the plant’s appearance. Control methods include:

• Setting out beer traps, which attract and drown the pests.
• Creating a barrier with abrasive materials like diatomaceous earth around the plant bed.
• Hand-picking slugs and snails after dark.
• Removing mulch or leaf litter where they hide during the day to reduce their numbers.

A less common pest is the weevil, a type of beetle that may chew small, notch-like holes along the edges of the leaves. This damage occurs after the plant has finished flowering and is usually not severe enough to cause significant harm. Because pest issues are often minor, widespread pesticide use is generally not necessary for maintaining a lily of the valley patch.

Toxicity Concerns

A significant issue with lily of the valley is its high toxicity. All parts of the plant—including the leaves, flowers, stems, roots, and the orange-red berries that appear after flowering—are poisonous if ingested. The plant contains cardiac glycosides, compounds that can severely affect heart function. This poses a considerable risk, especially in gardens frequented by young children or pets.

Ingestion of any part of the plant can lead to serious symptoms. In humans, this may include stomach pain, blurred vision, vomiting, a slowed or irregular heartbeat, and in severe cases, seizures or death. Consuming a small amount, such as two leaves, can be a fatal dose for a child. Dogs, cats, and horses are also highly susceptible to its poisoning, with symptoms including vomiting, confusion, and changes in heart rate.

Given the danger, extreme caution is advised. If ingestion is suspected, it is imperative to seek immediate medical or veterinary attention. Contacting a poison control center or heading to the nearest emergency room is the first course of action. For the safety of children and pets, it is recommended to avoid planting lily of the valley in accessible areas or to remove it entirely from the landscape.