How Can I Control Weeds In My Pond?

Do you want to control emergent weeds (cattail species, phragmites, purple loosestrife, bulrush, and alligator weed)?

Do you wish to control emergent weeds using the seasonal cutting & pulling method?

Do you want to control floating weeds (water lilies, duckweed, water lettuce, water hyacinth, spatterdock, and waterweed)?

Do you wish to control floating weeds using manual removal?

Do you wish to control submerged weeds (coontail, several pondweed species, bladderwort, hydrilla, Eurasian milfoil) using manual removal?

Do you wish to control submerged weeds using pond dyes?

Most emergent weeds reproduce via rhizomes. Because of this, simply cutting these plants is not enough, as the rhizomes will still be present and continue producing new plants. If done with the right timing, cutting can be an effective approach. Don’t cut them before July, as during this time they will be able to effortlessly resprout. Wait until July, August, or even September, when they won’t have energy available to resprout. You’ll have to repeat this for a few years, but each year you should notice fewer and fewer plants, at least in the case of cattails and phragmites.

While using chemicals shouldn’t be your first option because it can be harmful to other creatures like fish, in some cases herbicides are necessary. For plants such as cattails, phragmites, and bulrush, you’ll need to utilize a systemic herbicide, which is applied directly to the plant and works its way through the entire body of the plant, rhizomes and all. Glyphosate is affordable and efficient at treating emergent weeds, though depending on your location, the exact herbicide brand, and what you’re trying to control, you may need to either obtain a permit to apply the herbicide or contact a professional to do so for you.

Some floating weeds, like water lilies and spatterdocks, have rhizomes so you'll have to pull them from the soil in their entirety. Water lettuce grows atop the water without an extensive root system, so it can usually be removed by simply raking or skimming it from the water’s surface. Duckweed is very small and thus can be raked, vacuumed, or skimmed from the water’s surface without much effort. Simply adding more aeration to your pond to promote more water movement will also help prevent some floating weeds from being able to establish, as they typically prefer still water.

If weeds are more established, either a contact or systemic herbicide may need to be used. Some contact herbicides work quickly on a variety of emergent, submerged, and floating weeds, but do not remain in the water system for long before breaking down. This means there’s less risk of harm to your fish or other organisms.

Due to their soft stems, submerged weeds are among the easiest to remove by hand pulling, raking, cutting, or skimming. Trees could also be planted about the pond to help shade it and deter overgrowth – try to limit shading to only about 50 to 60% of your pond so that you don’t stunt the growth of native, desired plants.

You could utilize pond dyes to temporarily shade the pond long enough to kill off established weeds and prevent their regrowth. Eurasian milfoil is more aggressive than other submerged weeds, able to grow from even tiny portions of the plant that has broken off, so you’ll have to be very thorough when removing this particular species.

Though these species are easily manually removed, you can also utilize herbicides if they’re well-established and presenting a particularly persistent threat. There are seasonal herbicides available that can be applied once and will treat submerged weeds and some floating weeds for the duration of the season. This does, however, pose a potential threat as this means that the chemical persists in your pond for an extended period.