Aggressive lilies can quickly take over garden spaces, becoming persistent nuisances that choke out desirable plants. This problem is often caused by vigorous types, such as the common orange daylily or lily-of-the-valley, which possess specialized root systems designed for rapid expansion. Complete removal requires a targeted strategy that addresses these underground structures, as simply pulling the visible foliage is insufficient. Success depends on understanding the plant’s unique growth pattern and applying the correct removal method for its specific root type.
Understanding the Specific Lily Type
The first step in effective removal is correctly identifying the plant, as not all plants commonly called “lilies” share the same root structure. True lilies (Lilium genus) grow from a bulb, a fleshy storage organ that is generally easier to remove entirely if caught early.
Daylilies (Hemerocallis) are not true lilies and instead produce thick, fibrous roots and sometimes small tubers. These tubers store energy, allowing the plant to persist even after the foliage is cut back.
The most difficult to eradicate is often lily-of-the-valley (Convallaria majalis), which spreads through a network of underground stems called rhizomes. These rhizomes quickly colonize large areas, and any small piece left in the soil can readily sprout a new plant. The specific root structure—bulb, tuber, or rhizome—will determine the necessary depth and thoroughness of the removal process.
Mechanical and Cultural Removal Methods
For a non-chemical approach, thorough physical excavation remains the most reliable method for controlling lilies. Digging requires removing the entire root system, whether it is a bulb, a tuberous root clump, or a network of rhizomes, which can extend deep into the soil. Using a garden fork instead of a shovel is better, as it loosens the soil and reduces the chance of slicing roots into smaller, regenerative pieces.
When dealing with daylilies or lily-of-the-valley, dig down at least 12 to 18 inches and spread the removed soil onto a tarp. Carefully sift through this soil to ensure every root fragment, tuber, or piece of rhizome is collected, as a small remnant can lead to regrowth. All excavated plant material must be disposed of in sealed bags and not composted, preventing re-establishment elsewhere.
Smothering is a cultural control method that deprives the plant of the light needed for photosynthesis. This technique involves cutting the foliage down to the ground and then covering the area with an opaque barrier. Use thick black plastic sheeting, cardboard, or several layers of newspaper, extending the barrier beyond the infested patch. Cover the barrier with mulch or soil to hold it down and block out all light.
For smothering to be effective, the area must remain covered for an entire growing season to starve the underground root reserves of energy. A more intense form, solarization, uses clear plastic sheeting during the hottest months of the year to trap solar heat. This process effectively cooks the roots in the top layer of soil and must be left in place for at least six to eight weeks of consistent, high heat.
Strategic Use of Herbicides
When mechanical removal is impractical for large, established patches, a systemic herbicide can be used as a targeted strategy. A non-selective product containing glyphosate is chosen because it is absorbed by the foliage and translocated throughout the plant’s vascular system. The chemical travels down into the persistent roots and rhizomes, and must reach the entire underground storage structure to be successful against perennial plants.
The timing of application is crucial for the herbicide to be most effective. Apply the herbicide when the lily is actively growing and the leaves are fully developed, typically in the spring or early summer. During this period, the plant is actively moving sugars from the leaves down to the roots for storage, which maximizes the chemical’s translocation to the underground portions.
Exercise caution to prevent the herbicide from drifting onto desirable surrounding plants, as non-selective products will kill any green tissue they contact. Apply the product on a calm day when rain is not expected. Consider using a foam brush or wick applicator for spot treatments in dense garden beds. Due to the energy reserves of the tubers and rhizomes, two or more applications over a single growing season may be necessary for complete control.
Long-Term Monitoring and Regrowth Prevention
Lilies and daylilies are notorious for persistent regrowth even after thorough initial removal due to their energy reserves. The most effective long-term prevention strategy is to “starve” any remaining root fragments. This process requires vigilant monitoring and the immediate removal of any new foliage sprouts that appear.
The plant spends its stored energy to produce new shoots, which then begin to replenish the root’s carbohydrate reserves through photosynthesis. To prevent this energy replenishment, new sprouts must be severed or cut off at the soil line every seven to ten days. By consistently removing the leaves before they can photosynthesize, the underground root system will eventually exhaust its stored energy.
After the area is successfully cleared and no new growth has been observed for a full season, the space should be filled with desired plants or a dense ground cover. Planting non-invasive ground covers can physically outcompete any late-sprouting lily fragments by shading the soil and monopolizing water and nutrients. This proactive planting strategy helps maintain control and permanently occupies the space.