Controlling Duckweed – How To Kill Duckweed


By: Becca Badgett, Co-author of How to Grow an EMERGENCY Garden

Common duckweed (Lemna minor) is a rapidly spreading aquatic plant that deprives ponds of oxygen and leads to the death of fish and beneficial algae in still waters. It is important to get rid of duckweed for the health of your pond and existing aquatic life.

Duckweed Information

Duckweed is most often found in nutrient rich ponds, those where a buildup of leaves on the bottom creates stratification. Black, smelly ooze is a primary source of food for duckweed. Older ponds and those in quiet, undisturbed areas are likely candidates to need duckweed killer, as this is where the invasive, nuisance weed prefers to grow.

Duckweed is often accompanied by a similar, smaller plant called watermeal. The two work together to cover susceptible ponds quickly when proper conditions exist. It is important for duckweed control to begin as early in spring as possible. Successful duckweed control for ponds covered on the surface can take several years.

Duckweed can quickly take over the surface of the pond, decreasing oxygen levels necessary for fish and desirable aquatic plants to live there. Visiting Canadian geese, agricultural and animal lot runoff, lawn fertilizer and septic tanks that do not work properly contribute to high nutrient levels. Ponds that are naturally in motion by wind or moving water have fewer problems and need less duckweed control.

How to Kill Duckweed

The most effective and safest way of controlling duckweed is prevention. Natural ways of controlling duckweed can eliminate the need for chemical treatments, which may be required once the duckweed infestation has progressed.

Nutrient reduction in ponds aid in controlling duckweed, as does bubble aeration. Nutrient reduction deprives duckweed of what it must have to grow and spread and decreases the need for chemical duckweed killer.

Duckweed control includes the removal of leaf buildup on the bottom of the pond. Catch falling leaves in autumn before they reach the pond floor by placing netting or other material on top of the water as a partial means of duckweed control.

Controlling duckweed includes the physical removal of duckweed and watermeal plants. Wait for a windy day when the breeze can assist in controlling duckweed. When plants are pushed to the sides and edges of the pond, manually remove them with a long handled swimming pool net or other appropriate device that can reach the duckweed and scoop them out of the water. Manual removal alone is not enough to get rid of duckweed, but it can help with reducing the amount. This practice must be repeated.

Learning how to kill duckweed and preventing its buildup can keep your pond clear, unobstructed and help maintain a good environment for aquatic fish and plants. Aeration that reaches the bottom of the pond can disrupt the cycle of sediment buildup which encourages conditions appropriate for duckweed growth.

Biological Duckweed Control

Add natural predators of duckweed, such as Koi, grass carp, goldfish and domesticated waterfowl. Alone these biological controls cannot remove the problem, but if introduced to the pond before duckweed begins to grow, they can assist with duckweed control.

Get rid of duckweed before it takes over the pond by increasing aeration at the bottom, manually removing plants from the surface, and reducing nutrients that create bottom sediment. Try a combination of these methods before resorting to chemical duckweed control.

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How do you get rid of duckweed in a lake?

Herbicides will remove duckweed quickly, but are NOT recommended for ponds with fish. One of the easiest methods of removing duckweed is with chemical herbicides, which destroy the plants at the cellular level. The issue with treatments such as this is they're extremely toxic to pond fish, plants, and wildlife.

Additionally, will vinegar kill duckweed? Vinegar can kill some types of pondweeds and algae. However, it is not very effective for duckweed. Although vinegar is safe for fish and other pond habitats, you shouldn't use a large amount of it at a time in the pond.

In this way, how do I get rid of duckweed without chemicals?

Biological Duckweed Control Get rid of duckweed before it takes over the pond by increasing aeration at the bottom, manually removing plants from the surface, and reducing nutrients that create bottom sediment. Try a combination of these methods before resorting to chemical duckweed control.


Manual Removal

Wear a pair of hip waders and carefully enter the body of water. For small garden or ornamental ponds, stand at the edge of the pond.

Grasp the handle of a pool skimmer and skim the surface of the water with it. This will scoop the duckweed out of the water. Pull the pool skimmer back towards you and onto the bank.

Lay a large garbage bag on the ground. Smack the pool skimmer lightly against the garbage bag-covered ground to dislodge the duckweed from the skimmer. Alternatively, rinse the duckweed off the pool skimmer with a hose. Remember to keep the removed duckweed far away from the body of water to prevent regrowth. You can also add duckweed to your compost.

Continue in this manner until you have removed the duckweed from the water. Repeat the process as new duckweed appears.


Identifying Duckweed (Lemna Minor)

Duckweed is one of the smallest flowering, free-floating plants found around the world. Measuring just 1/16" to 1/4" in length, duckweed floats on the water surface in colonies not attached to the bottom. Duckweed floats wherever the wind or currents take it, absorbing nutrients from the leaf undersurface and a very fine root hanging from it.

Duckweed can have one leaf or up to three leaves, known as fronds, about the size of a pencil eraser head, with a single root hair.

Duckweed prefers eutrophic, motionless fresh water in wetlands, ponds, lakes and slow moving streams. Duckweed requires a lot of nutrients to grow - especially nitrogen and phosphorus. Major sources of nutrients include Canada geese, lawn fertilizer, agricultural run off, leaking septic systems, and tree leaves.

Our POND Solution products contain the best products to control duckweed and algae, including effective herbicide and nutrient reducing treatments.


How to Get Rid of Duckweed in a Pond

Duckweed is also known as Lemna Minor, and can be found in freshwater ponds and moving streams. Duckweed can grow easily in ponds that have high nutrient levels and spread quickly. The weed is also called duckweed because it is often a food resource for ducks and other animals. However, most people see the floating, dark green weeds as an eyesore for their ponds. The duckweed is beneficial if your pond is full of weed, and many pond experts would recommend leaving at least some duckweed in the pond. Remove all of the duckweed if you don’t have any fish or want wildlife in your pond.

Put a hose in your pond and over flood the pond with water if you have no fish in it. Let the duckweed flow out of the pond and then dispose of it all in a plastic bag. Make sure to wear latex gloves when handling the duckweed.

  • Duckweed is also known as Lemna Minor, and can be found in freshwater ponds and moving streams.
  • However, most people see the floating, dark green weeds as an eyesore for their ponds.

Use a pool cleaning net to scoop any excess duckweed that may be stuck to the sides of your pond. If you have fish in your pond and only a small amount of duckweed to remove you also just use a net to remove the duckweed.

Remove all fish and drain your pond entirely for severe cases of duckweed that need to be eradicated. Clean your pond out using disinfectant cleaner and wash out the bottom completely using a hose.

Refill your pond with water and check the alkalinity of your pond by using test strips which can be purchased at you local pool cleaning or lawn care store. Add crushed limestone to your pond if the alkalinity is below 100 mg.

Add fish to your pond that will feed on the duckweed. Koi are the best to add and will eliminate the duckweed problem. However, the duckweed shouldn’t return as long as you keep your pond clean and healthy.


Watch the video: How to Get Rid of Duckweed and maybe why you shouldnt: The Good. The Bad


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