Water lilies are aquatic plants often cultivated for their floating leaves and blossoms. When left unchecked in a pond, their rapid spread can lead to overgrowth, covering the water surface. This excessive coverage restricts light penetration and interferes with recreational use. Controlling these plants requires understanding why they flourish and applying a combination of physical, chemical, and long-term strategies.
Why Lily Pads Thrive
The proliferation of water lilies is directly connected to a pond’s environmental conditions, particularly nutrient availability. An excessive supply of phosphorus and nitrogen, often introduced through stormwater runoff, fuels rapid plant growth. These nutrients are easily absorbed from the pond sediment, allowing the plants to expand their dense root systems.
Shallow water depths also create ideal conditions for establishment. As ponds accumulate sediment, the shallower edges become perfect anchoring points for the plant’s robust rhizomes. Abundant sunlight further contributes to their success, promoting the photosynthetic activity necessary for their large, floating leaves.
Physical Removal Strategies
Effective physical control focuses on removing the entire plant structure, anchored by stout, horizontal root systems called rhizomes. Cutting the floating pads at the water line is ineffective because the plant quickly regenerates new leaves from the submerged rhizome. For long-term success, the entire root mass must be pulled from the pond bottom.
Specialized tools like aquatic cutters, rakes, or weed rippers are designed to sever and pull the tough, fibrous rhizomes. Manual removal or dredging may be necessary for small areas or fully established colonies. All removed vegetative material must be collected and disposed of on land, as leaving it in the water allows fragments to re-establish or release nutrients back into the ecosystem.
Targeted Chemical Control
The use of EPA-approved aquatic herbicides offers an effective method for controlling extensive lily pad infestations. Herbicides are categorized by their action, with systemic products being the most beneficial for long-term control. Systemic herbicides, such as those containing glyphosate or 2,4-D, are absorbed by the leaves and translocate down to the rhizomes, killing the entire plant structure.
Contact herbicides, like diquat, act faster but only destroy the plant tissue they directly touch, requiring repeat applications to exhaust the root system. When applying any herbicide, safety protocols must be followed, starting with reading the product label. A significant risk of chemical treatment is the rapid decomposition of dead plant matter, which consumes dissolved oxygen and can cause a fish kill. To mitigate this danger, treat no more than one-third of the pond’s surface area at a time, allowing a two-week interval between applications for the water to recover.
Long-Term Pond Management
Sustained control relies on reducing the environmental factors that encourage water lily growth, particularly the nutrient load. Establishing a vegetative buffer zone of native grasses and plants around the pond’s perimeter is an effective strategy to filter runoff. This buffer, ideally three to five feet wide, absorbs excess phosphorus and nitrogen before they enter the water.
Implementing an aeration system, particularly a bottom-diffused model, helps maintain healthy dissolved oxygen levels. Aeration facilitates the aerobic digestion of organic sludge on the pond bottom, which locks up nutrients and prevents them from feeding aquatic plants. The application of aquatic dyes is another preventative measure, tinting the water to block sunlight and inhibit the growth of submerged plants and algae. Biological controls like triploid grass carp are not effective against water lilies, as the fish do not prefer their tough, fibrous leaves.