Q: I have a lot of water lilies in my 1/2 acre pond. How do I control them?
Dan – Newnan, GA
A: In ornamental ponds, water lilies planted in pots are prized possessions—but in a shallow farm pond or lake, lilies living wild can be an invasive species that takes over the water surface in no time.
Of course, water lilies aren’t all bad. Their leaves and roots provide food for beaver, moose, muskrat, porcupine, and deer. Their seeds are gobbled by waterfowl, and their leaves provide protective coverage for largemouth bass, sunfish, and frogs. Left unmanaged, however, water lilies can restrict lake-front access, eliminate swimming opportunities and quickly take over shallow areas.
But before we get into how to control these beautiful but troublesome aquatic plants, let’s learn a bit about them.
The water lily is a floating-leaved aquatic perennial herb that grows rooted in mucky or silty sediments in water 4 to 5 feet deep. It prefers quiet waters like ponds, lake margins and slow streams. When unmanaged, the plant tends to form dense areas covering hundreds of acres.
Each spring, new shoots appear from the rhizomes and grow up through the water until they reach the surface. The flowers appear from June to September. Each blossom opens in the morning and closes in the early afternoon for two to five consecutive days. After the flowers have closed for the final time, the flower stalk corkscrews and draws the developing fruit below the water.
The plant over winters underground as the rhizome. These rhizomes, along with the plant’s seeds, are how it reproduces. A planted rhizome can grow to cover a 15-foot-diameter circle in just five years!
Limiting Those Lilies
You can control water lilies with several different methods.
- Mechanical Control: First, you can cut/harvest the water lilies or dig up the rhizomes to create open areas of water. If you cut the lilies, you must do so several times a year as these plants thrive in shallow water and grow rapidly. If you dig up the rhizomes, it can be an intrusive and costly though permanent process; they can be difficult to dislodge, but it can be done via rotovation (underwater rototilling) or excavation. Either way, mechanical control is a difficult method because the plant will likely regrow from seeds or remaining rhizomes.
- Chemical Control: Another more effective method is to use reactive chemical treatment, like Shoreline Defense®, to manage lilies that are actively growing and have reached the surface. When applied directly to the foliage—along with some Treatment Booster™ PLUS to break down the plant’s protective surface—the herbicide’s active ingredient penetrates the lily and makes its way to the rhizome. Once it has turned brown, use a Weed Cutter to remove as much of the decomposing plant as possible to prevent an accumulation of dead material and muck. If you use this method, treat your pond in sections, dosing only half of the lilies at a time; if the weather is hot, decrease that to a third or quarter, waiting 10 to 14 days between treatments.
- Preventive Control: In addition to mechanical and chemical control, you can also prevent—or at least slow down—the growth of water lilies by treating the pond’s water with Pond Dye. By blocking the sun’s rays early in the season, the lilies will not get the light they need to develop.
Controlling water lilies can be a challenge. But these methods, you can manage them and keep them contained in a particular area, making them a beautiful addition to your landscape.
Pond Talk: How do you control wild water lilies in your farm pond or lake?