From our standpoint as water lilies, a complete cover of the pond surface is not a problem; it is the ultimate sign of a thriving colony. Our large, flat leaves, or pads, are engineered by evolution to capture the maximum amount of sunlight, which is the essential fuel for our growth and reproduction. When our leaves cover the entire surface, we have successfully outcompeted other plants for this vital resource, shading the water column below and preventing the germination of submerged competitors. This canopy also helps to stabilize water temperature and reduces algae growth by limiting light penetration. Our expansive coverage is a testament to a healthy root system in the pond's sediment, where we absorb nutrients. Essentially, a full pond surface is our natural and desired state, a successful conquest in the plant world.
While beneficial for us, an absolute monopoly can have unintended consequences for the broader pond environment. The most significant issue is gas exchange. The entire surface of the water acts as a lung for the pond, allowing oxygen to dissolve into the water and harmful gases like carbon dioxide to escape. When our leaves form an impenetrable mat, this process is severely restricted. This can lead to dangerously low oxygen levels for fish, beneficial bacteria, and other aquatic life, especially during the night when plants respire and consume oxygen. Furthermore, the deep shade prevents light from reaching submerged oxygenating plants, which would otherwise help replenish oxygen, creating a negative feedback loop. The pond's health can begin to suffer as a result of our success.
To maintain a balanced ecosystem where we can flourish without causing harm, selective removal of our leaves is necessary. The most effective method is simple, manual pruning. The goal is not to eradicate us but to thin the canopy. Using sharp secateurs or a knife, you should cut our leaf stems well below the water surface, several inches from the base of the plant. It is crucial to remove the entire stem fragment to prevent it from decaying in the water. Focus on removing the older, yellowing, or damaged leaves first, as these are less efficient at photosynthesis and are nearing the end of their life cycle. Aim to clear approximately one-third to one-half of the pond's surface area, creating open water patches. This allows for sufficient light penetration and gas exchange, ensuring the vitality of the entire pond, which in turn supports our long-term health.
If our colony becomes too dense year after year, the issue likely originates at our root structure. We grow from thick, fleshy stems called rhizomes that spread horizontally in the planting containers or pond bottom. Over time, these rhizomes become congested, leading to smaller leaves and flowers as we compete with ourselves for space and nutrients in the container. The long-term solution is to divide our rhizomes. This is best done in late spring or early summer when we are actively growing. You would need to lift our container from the pond, remove the plant, and using a sharp knife, cut the rhizome into sections. Each section must have a growing point (or "eye") and some healthy roots. Replant the most vigorous divisions in fresh aquatic soil and return them to the pond. This process rejuvenates us, encourages larger, healthier leaves and more abundant blooms, and naturally reduces overcrowding for several seasons.
Another strategy to prevent our complete dominance is to introduce other floating or emergent plants that can compete with us for space on the surface. Plants like water hyacinth or water lettuce are fast-growing floaters that will occupy surface area, naturally limiting the space available for our pads to spread. Emergent plants like pickerelweed or iris grow vertically, breaking up the flat canopy and adding structural diversity. From a plant's perspective, this creates a more diverse and resilient plant community. While we may not appreciate the competition, a mixed planting scheme reduces the need for frequent human intervention and creates a healthier, more stable aquatic environment where no single species, including ours, can overwhelm the system.
