How do you get rid of duckweed in a pond?

Contents

Duckweed

Description

Duckweed is a very small floating plant. It has shoe-sole shaped leaves with a small hair-like root hanging below. It resembles a four-leaf clover approximately the size of a pencil eraser. Duckweed in ponds is frequently misidentified as algae. Once established, duckweed in ponds can cover the entire water surface and resemble a golf course green. It can cut off sunlight to submersed plants and cut off oxygen to fish and other wildlife. If you need to begin duckweed control, read below.

Mechanical Control

One duckweed control method is by raking or skimming it off the pond’s surface.

Duckweed typically prefers stagnant and slow moving water. By adding an aeration system, you can eliminate Duckweed completely or limit the growth to the edges which are easily reachable with a hand skimmer.

Chemical Control

There are several options to control duckweed in ponds.

  1. Use a season long herbicide such as Airmax® WipeOut™ or Sonar™ A.S.. One treatment treats the entire body of water for duckweed and many other common pond weeds for the season.
  2. Use a broad spectrum contact herbicide, such as Ultra PondWeed Defense®, will quickly kill duckweed. Because it does not stay in the water body, multiple treatments may be needed throughout the season.
  3. Use Propeller™, a fast and selective herbicide that controls tough invasive and nuisance aquatic plants.

Chemical Application Best Practices

Anytime you use chemicals treat weeds and algae, please keep in mind the following:

  • When beginning duckweed control, treat your pond in sections. Treat only half the pond’s surface at a time. During hot weather or when treating heavy growth, it is important to treat no more than ¼ of your pond at a time and wait the full 14 days before re-applying. This helps lower the risk of fish loss during hot weather or when treating heavy growth.
  • Once the weeds have browned, use a rake to remove as much dead material as possible. This prevents an accumulation of dead plant material and muck.
  • Take a proactive approach to pond management. Use PondClear™, MuckAway™ and Pond Dye to keep your pond looking great. For more information, see our article on the Airmax® Ecosystem™

Ask an Expert

If you are unable to identify your pond weed(s) using our Weed ID Guide, follow this article to email us a photo.

Duckweed Control: How To Get Rid of Duckweed In A Pond Naturally

by Tory Jon | Last Updated: January 25, 2020

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Duckweed can deprive your pond of precious oxygen causing the death of good algae… and potentially your fish!

So, it’s important to rid your pond of duckweed as quickly as possible for the health of your pond ecosystem.

Let’s take a look at how to easily get rid of duckweed and keep it from coming back!

Psst! Pin This Page For Future Reference

What Is Duckweed?

Duckweed (Lemna Minor) is a very small aquatic plant that floats on the surface of your pond. It is considered a nuisance for a number of reasons and is often mistaken for pond algae.

It appears as a small green leaf (known as a frond) from the surface with a small root hanging below that resembles a hair. There can be between one and three fronds in total, with the largest fronds being up to a quarter of an inch in size. The appearance is quite similar to blanketweed, but duckweed is a plant where blanketweed is algae.

Did you know…

Duckweed is being studied as a potential source of clean energy. It actually reduces the amount of carbon in the air, instead of adding to it like fossil fuels.

If allowed to establish itself, this tiny aquatic plant can reproduce and cover the entire surface of your pond. As it is a similar color to grass, this can present a danger for those who are not aware the pond is there.

Full or even partial coverage can block sunlight from reaching underwater plants and can result in the pond water becoming deoxidized. This presents a problem for both animals and plants in the pond, as oxygen is required for them to survive. It also affects the growth of beneficial bacteria in the water, further damaging the pond ecosystem.

The growth of the plant also requires nutrients from the water. In certain instances, this will reduce the amount of nutritional matter available for other pondlife.

Eliminating a duckweed infestation, or any pond weed infestation for that matter, should be done promptly in order to ensure the continued health and well-being of your pond environment. There are a number of methods for controlling and removing duckweed, some of which are more effective than others.

How Does Duckweed Grow?

Duckweed is a plant and so needs the same environment as any other plant to grow. When ponds are nutrient rich the growth of any aquatic plant will be promoted, and not just those that you want to grow.

More specifically, ponds with a buildup of leaves and other old plant matter on the bottom of the pond create the most ideal conditions for duckweed to begin to grow. The decomposition of organic matter at the bottom of a pond release chemicals and nutrients that are perfect to encourage the growth of duckweed.

Other contributing factors to nutrient provision can include visiting animals (including birds like Canadian geese), lawn and plant fertilizer, agricultural runoff, and even leaking septic tanks.

Old static ponds are the most susceptible kinds of pond to duckweed infestations. The lack of surface movement causes the water to become stagnant and allows the duckweed to settle – ponds that feature moving water or are even in windy areas are less likely to be filled with duckweed.

Duckweed is often found in conjunction with watermeal, which is an even smaller (but similar) plant.

Did you know…

Watermeal is the smallest flowering plant in the world and looks like little green grains of cornmeal.

If both of these plants take hold, it can be a long process to get rid of them as they can easily take over the entirety of the surface of a pond – no matter how large it is.

And as you can see in the video below, it doesn’t take long for duckweed to grow!

By minimizing the potential for duckweed to grow, you will hopefully be able to prevent major infestations. Keep the water in motion where you can and keep the pond clear of any external sources of nutrients as far as possible. This can even include reducing the amount of food given to fish, as overfeeding fish will introduce nutrients to the water and enable duckweed to grow.

Prevention of duckweed is certainly easier than fixing an infestation. There are several methods for used to control duckweed in ponds that require varying amounts of physical effort and ability. Let’s look at those now.

How To Control Duckweed

Fully eliminating the potential for duckweed to grow is virtually impossible, but there are methods for making it easier to control.

As duckweed grows quickly in still water that contains nutrients – preferably stagnant water – the simplest method to prevent this from occurring is to install a pond aeration system.

This will have the effect of completely eliminating the duckweed, or at least making it manageable. The only potential areas for growth with an aeration system will be right near the edges of the pond, where it can be easily removed manually.

Dissuade birds to visit your pond wherever possible and be careful when tending to the plants in your garden. One simple mis-spray with a fertilizer applicator and the pond will have a sudden boost in nutrients. While one spray might not prompt duckweed growth, continually spraying the pond with fertilizer will, and so care should be taken at all times.

If you have a septic tank, make regular checks on it and ensure that it is kept in good condition. A leak might start off as a minor inconvenience, but for the safety of your local environment, you should get it repaired as soon as possible. The leak will also spread nutrients that duckweed can use to grow in a pond, so if you want to keep duckweed under control, keep your septic tank in good repair.

Keeping your pond clean is another good method for reducing the kinds of nutrients duckweed needs to grow. If you have a buildup of plant matter, vegetation, and leaves on the bottom of your pond, remove them. The rotting matter releases everything that duckweed needs to grow quickly, and you should attempt to avoid that at all costs.

Duckweed needs to be controlled as soon as possible. From a single plant, a new plant can be produced every 24 hours under the right conditions. While this may not sound like a lot, consider that 2 become 4, and then 8, 16, 32, and so on. Within 14 days, you could have over 16000 plants growing if you haven’t taken preventative measures. If that doesn’t sound unmanageable, remember the next day you could have 32000, then 64000…within 20 days you could be theoretically be bordering on 1 million plants!

It’s unlikely to work exactly this way in real life but be aware that the potential for massive reproduction and growth is there from the start. And you might not always start an infestation with just a single plant…

How To Get Rid Of Duckweed

Preventing or reducing the possibility of duckweed growing in the first place is the best method for controlling duckweed, but should it begin to grow you’ll need to get rid of it.

Duckweed can be removed by physically taking it out of the water or using a selection of treatments on it. Some of these treatments are chemical based, where others are natural and organic, and even safe for fish.

The size of the infestation may help determine which method to use. If there are only a few plants, manual removal is the easiest method as it can be done immediately, and even by hand without special tools. Of course, duckweed removal tools are available to make the job easier.

A single session of manual removal is unlikely to extract all the duckweed plants, and so it is wise to repeat the process regularly. If you have aerated your pond water, this process will become easier as the new growth should occur nearer to the pond sides.

Duckweed can also be controlled with organic methods including the introduction of natural predators of the plant to eat it up.

The final and most drastic measure is chemical control to remove the duckweed infestation. While this can be effective – and if the pond is absolutely covered it may also be necessary – it is best to avoid using chemicals in the first place due to the potential effect on the environment and local wildlife. Chemicals can have a harsh effect on the pond, and may also damage plants that you want to survive. If you keep fish in your pond, it is also advisable to check on what effect any chemicals may have on them.

Using one or more of the other non-chemical methods to control and remove duckweed is preferable, and chemicals should only be used as a last resort.

Duckweed Removal Tools

Visible duckweed can be removed by hand – literally by dipping your hands in the pond and lifting it out. While this method isn’t the best way to get rid of duckweed, it can be used in an emergency.

A far better solution is to use a tool to aid in the duckweed removal process. A pond rake or net are both good options, allowing you to either bring the floating duckweed closer to the edge to enable easier access or to lift it out of the pond altogether.

Different sizes and shapes of netting are available, but extra-fine nets are recommended as those with larger holes will allow the duckweed to slip through.

A floating boom can be used on larger ponds to skim the surface and draw the duckweed to the side, as can a parachute skimmer.

Once the duckweed is within reach, it can be removed from the surface of the water with a net or by hand.

Another alternative is to use a pond vacuum to remove the duckweed from the surface, and also to help remove any debris from the bottom of the pond to prevent further growth.

Organic Duckweed Control

Controlling duckweed by use of organic methods is preferable to the use of chemicals and may be easier, and more effective, than constantly raking and using a net to empty your pond.

Some animals enjoy eating duckweed, and so you may find it beneficial to introduce these animals to your pond or water garden. Goldfish, Koi and grass carp, as well as domesticated waterfowl, will eat duckweed.

They are not capable of removing a large infestation (as their appetite will not be big enough), but should you have no duckweed or have recently cleared your pond, these animals will keep the duckweed under control.

To further control duckweed, ensure your pond water is aerated towards the bottom, and try and maintain surface disturbance too.

A fountain or water feature (like pond spitters) can be effective for this. Even with this in place, continue with manual removal where necessary. Keeping the pond clean and free of rogue nutrients is an effective combination with these animals present.

Another option to consider is the use of pond dye. This natural product will not affect any wildlife but will change the color of the pond water. This serves a double effect of making the pond look more attractive, while simultaneously reducing the penetration of UV light below the surface. This will slow the breakdown of any organic matter at the bottom of the bend, thereby reducing the nutrients in the water and slowing the growth of duckweed.

Planting towards the south side of the pond can also help reduce the growth of duckweed by providing shade and slowing the photosynthesis process. Other surface-floating pond plants (for example, waterlilies) can also reduce the amount of duckweed.

Pond bacteria additives are available that contain bacterial cultures that will remove nutrients from the water. This will, of course, restrict the growth of duckweed, but always care should be taken if you keep fish or other aquatic animals.

Chemical Duckweed Control

Depending on the severity of your infestation, you may have to resort to chemical control. Rules and regulations vary from state to state, so it may be difficult to obtain “weedkiller” products if you are an amateur pond keeper. There are usually very strict and exact processes and guidelines to follow if you wish to use such a product.

Far more common are chemical herbicides which are effective in the removal of duckweed but generally less damaging to the environment – note they are less damaging, which is not to be construed as “good for”.

These aquatic herbicide products kill duckweed at the cellular level, but be careful as some can be toxic for fish, plants and other aquatic species. They are designed to destroy and kill, and so must be used with care and treated with respect.

Some herbicides may be considered safe for fish and other animals, but always read the label, and always be certain before applying any herbicide treatment to a pond containing animals of any kind. You will only get one chance to avoid a potentially devastating mistake.

Herbicides come in three main varieties – whole pond herbicide, contact herbicide, and selective herbicide.

The first, whole pond herbicides, will work for a whole season in your pond. Applying one treatment will protect the entire pond, killing any weeds including duckweed, and requiring no further treatment or maintenance.

The second variety is a contact herbicide which is applied to the weed itself. A contact herbicide does not stay in the water to kill further infestations, so you may need to perform multiple treatments throughout the year to control duckweed.

The third variety is known as a selective herbicide. This can be mixed in the water and will target particular types of aquatic plants, including duckweed. Non-selective herbicides will attack and destroy any plant matter they come into contact with.

Bear in mind that using an herbicide will not remove duckweed from your pond, they will only kill it and prevent further growth of that particular infestation. To fully remove the duckweed, it is easiest to work on your pond in sections.

Treat your first section and wait for the duckweed to die – it will turn brown as it dies. Use a rake and net to remove as much of the dead section as possible, and then move on to the next section of your pond.

Once you have treated the entire infestation and removed all the dead matter possible, you can repeat the process again to remove any still-remaining duckweed growth.

Depending on how much duckweed you had to start with, this may take several cycles to complete. Different herbicides will potentially have different cycle lengths – always read the label to make sure. Applying a second treatment too soon could have an adverse effect on your pond, including any animals or plants living in and around it.

Removing the dead matter from the surface after treatment is important for two reasons. First, it allows you to see any living growth underneath the dead sections, and second, it prevents the dead mass from sinking and rotting at the bottom of the pond. This would be counterproductive as it would produce more nutrients during the decomposition process that would enable further duckweed growth.

Duckweed is one of the most common pondweed problems. They grow quickly and takes a little time to cover up the whole pond.

Although, duckweed is a portion of good natural food for some fish species, if present in excessive amounts, it can hart the pond environment and its habitats. Therefore, controlling their population is a must.

There are several methods of controlling and removing duckweed in a pond or lake. In this article, I will talk about some of the easiest and effective methods that you can apply to get rid of duckweed in pond.

Table of Contents

7 Ways to Control Duckweed in Pond and Lake

Stock Duckweed Eating Fish

There are many species of fish that feed on aquatic vegetation. But not all of them are effective for duckweed control. This is because most of them will not eat duckweed if they got enough supply of other normal food.

Grass Carp

Grass carp is the most popular species of fish for aquatic weed control. They primarily feed on aquatic plants. Grass carp can eat up to three times their body weight per day.

If you found that less than 50% of your pond is covered with duckweed, then stock 10 grass carp of 8-12 inches per acre. For coverage more than 50% the number will be 15-20.

Tilapia

Tilapia is also a good fish to stock in your pond or lake to control the duckweed. Note that, there are two verities of tilapias, the blue one and the red belly one. You should stock the red belly tilapias because the blue one doesn’t eat duckweed.

Stock up to 30 pounds of small tilapias in one acre. You might also need permission from the eligible authority for stoking tilapias.

Goldfish

If you have a small garden pond then you can have some goldfish in it to control the duckweeds. Duckweed is a favorite food of goldfish. Once you stock some of them in your garden pond, they will finish any duckweed or watermeal.

Koi Fish

Most of the garden pond owners stock koi fish for their beauty. But koi is also good for controlling duckweed in a pond.

You may also find that your koi don’t eat duckweed at all. The reason is simple – they aren’t hungry enough to eat duckweed. What you can do as a solution is to cut their regular food supply to some extent. They will surely eat up the duckweeds.

Have Some Domesticated Duck For Eating Duckweed

Do you know why we call it duckweed?

Because duckweed is the favorite food of duck. Also, wild duck is the source of duckweed in your pond as I have told you earlier.

If you have no problem with keeping ducks, then you can have some domesticated ducks in your pond. The ducks will keep in the population of the duckweed in a tolerable limit and you will also get some eggs for free. But don’t forget to feed your duck some extra food twice a day. Also if you have small fish in your pond, you have to think twice before you release the ducks. Ducks can eat them up also.

Use Floating Drag Rope or Net to Collect and Remove Duckweed

Duckweed Removal with Floating Net Credit: Adam Byer Koi

If you want to remove duckweed from a large pond or lake, you can use floating drag rope or net. It is an effective and efficient method. This is also very cost-effective and you can make the rope at home.

First, place the rope near the shoreline and close the loop. Then slowly decrease the area and the duckweeds will be dense in that small area.

After that, you can remove them by hand or pond net. Make sure you put the duckweeds far from the pond so that they don’t come back to your pond again.

Use a Pond Net to Collect Duckweed For Your Garden Pond

If you are a small pond owner, you can adopt this method. Use a pond net or pool leaf collecting net for collecting the pondweeds.

Here the wind can help you. When the wind blows, the duckweeds are gathered in one place. From there you can collect them.

When you select a pond net, go for the large one. It will make the job easier.

Use a Mechanical Duckweed Skimmer for Skimming Out Duckweed

Mechanical pondweed skimmer is a motor-driven pond skimming system. It is efficient and eco-friendly.

The working mechanism of a surface skimming system is straightforward. It pumps out the surface water from the pond along with the duckweeds. Then the water goes through a strainer. The strainer separates the water from the duckweeds or any other solids. Then the clean water again goes back to the pond.
You can use a surface skimmer if you have a large pond and budget.

Again for small to medium ponds, low-cost pond skimmers are also available. They are available in two models, regular pond skimmer and floating pond skimmer.

The regular pond skimmer is installed outside of the water. Water is pumped out of the pond and sent to the skimmer. The strainer or mesh separates the duckweeds from the water.

The floating skimmer is placed at the pond. When it runs it pusses the surface water through it and the floating duckweeds are strained in it.

Use a Parachute Skimmer for Collecting Duckweed

Parachute skimmers are newly introduced and an easy to use tool for duckweed removal. It has mainly three parts. The mesh screen that retains the duckweeds. A floating device keeps it above the water. And the rope is used to drag it to the shoreline.

This tool is very easy to use. All you have to do is to throw it to the water with pondweed and drag it to the shore by rope. Then you have to collect the duckweeds from the mesh.

Parachute skimmers can be 3 meters wide. You can use this for the effective removal of duckweed in small and medium ponds.

Use Chemical Herbicides That Will Kill Duckweed

Many aquatic herbicides are available that works effectively on duckweeds. I recommend the following herbicides that are tested by the MDC. You can get a pdf copy of their duckweed and watermeal control guide here.

Sonar AS

Sonar AS is a trading name. The chemical name is Fluridone. It is the safest aquatic herbicide that you can use to kill the duckweed in your pond. Sonar AS doesn’t bring any harm to the pond environment.

The application rate of Sonar As is .25 to .5 Gal per surface acre or as per the manufacturer recommendations. There is no restriction on fish consumption and water use of livestock and swimming.

Reward and Weedtrine-D

One of the fastest ways to kill the duckweeds is to use Reward or Weedtrine-D. Reward and Weedtrine-D are the trade name and the chemical name is Diquat. The action is fast as duckweed absorbs it quickly.

The rate of application is 1 to 2 gallons per surface acre of 2L or as per manufacturer recommendation. There is no restriction on fish consumption. But you have to wait at least 5 days to use the water for irrigation, domestic and cattle use.

Cutrine Plus

Cutrine Plus is Copper Ethanolamine Complex. It is widely used in fish ponds and hatcheries for controlling algae and duckweed. It kills duckweed by braking the cellular structure.

If you have trout in your lake or pond, then you have to be cautious while using it. Because of the carbon hardness of water is less than 50 ppm, it can be toxic to trouts.

Before you use any aquatic herbicide in your pond or lake, make sure it is safe and don’t use a overdoes.

How do you get rid of duckweed naturally?

The natural duckweed control method works best when the population of duckweed isn’t very high in the pond. You can follow the following preventive measure to get rid of duckweed naturally.

  • Give your fish the exact amount of food that can eat. Excess food increases the amount of nutrition in water which triggers the growth of duckweed.
  • Stock duckweed eating fish and domesticated duck in your pond or lake.
  • Don’t let leaves fall in the pond and collect the falling leaves. They increase nutrition in water which helps duckweed growth.
  • Use barley straw. It is a good method of controlling it.

Frequently Asked Question (FAQ)

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. That can be harmful to the fish. So it is not a good way to control duckweed with vinegar.

Should I remove duckweed?

It depends on the population of duckweed in your pond. If the population of duckweed is very high, say more than 1/4th of your pond is covered with duckweed then you should definitely remove them. Duckweeds are beneficial for your pond when they are present in a small number.

Is duckweed good for a pond?

Duckweed is good for a pond for many reasons when they are present in a moderate number in your pond. Some of the benefits of duckweed are –

  • They are good natural food for some of the fish like Koi, Goldfish, and Grass Carp.
  • Duckweed is a good natural filter for a pond as it can absorb bad materials out of water.
  • It gives shade to the pond.
  • Working as a cover, it can save the fish from the predators.

Does copper sulfate kill duckweed?

No, Copper Sulphate alone can’t kill duckweed. But you can use Copper Sulphate along with Diquat. This gives the best result when you want to use a chemical herbicide to control duckweed.

Does duckweed die off in winter?

Yes, duckweed dies off in the cold weather. But there are some species of duckweed that can produce spores. These spores can survive the winter and produce new duckweed when the winter is over.

Does barley straw get rid of duckweed?

Barley straw doesn’t directly kill duckweed. But it works to some extent to keep their population in control. therefore, it can be a good way to control duckweed in a pond.

How do I get rid of duckweed in a large pond?

Treating duckweed in a large pond can be tricky. You can adopt the following control and removal method for getting rid of duckweed in a large pond.

  • Stock duckweed eating fish.
  • Collect and remove them with an effective collection system like a large net or skimmer.
  • Kill them using a duckweed killer.
  • Keep the amount of nutrition in your pond low so they don’t grow quickly.

Why is duckweed bad?

Excessive duckweed in pond and lake are bad for a number of reasons. They create the following problem –

  • It blocks the sunlight from reaching the pond water.
  • It houses the bad insects and disease creating organisms.
  • Dead duckweed creates a lot of debris in the pond that finally result in an algae bloom.
  • It boosts the growth of anaerobic bacteria that are harmful to the pond.
  • Prevents the growth of good algae and submerged pondweed that oxygenate the pond water.

How fast does duckweed multiply?

Duckweed grows really quick. It enough nutrition is available in water it can divide once a day. A couple of duckweeds can cover the whole pond within one and a half months.

Will duckweed kill fish?

Although duckweed will not directly kill fish, its long term effect can result in fish death. It can heavily contaminate the pond water and create a lack of oxygen in the pond water. This can lead to fish death. Also, this facilitates the housing and growth of disease creating organisms that can cause fish death.

Does duckweed oxygenate water?

Duckweeds are any good for oxygenating water. As duckweed are floating pond plants, the oxygen they deliver goes directly to the air, not in the water because photosynthesis occurs in the upper layer. For oxygenating pond water, submerged pond plants help the best.

Where does duckweed come from?

Many pond owners wonder, where did they end up getting so much duckweed in their pond when they haven’t released any duckweed themselves. But duckweed can migrate to your pond in many ways that you might not think of. Like –

  • Most of the time duckweed is carried by the wild waterfowl. While roaming in the source, duckweed is attached in their body. Again when they come to your pond, they leave duckweed in your pond from where it grows and finally covers up your pond.
  • Another source of duckweed is the pond plants collected from sources where duckweed is present.
  • If you take any pond maintenance service, their instrument can be a carrier of duckweed.

It is better you prevent duckweed from entering your pond rather than controlling and removing duckweed when they have covered up your pond. So, take the necessary measures so that you don’t face this problem in the future.

I hope these methods will be helpful for you for duckweed control.

Frog in Duckweed, photo by StevesPhotos.com

A Weed Most Fowl

Do ducks eat duckweed? Yes and no. Do humans eat duckweed? Yes and no. Domestic ducks tend to eat duckweed, wild ones don’t. Humans can eat duckweed but …

Wollfia, Watermeal

Generally said there are three genera of duckweeds: Lemna, Wolffia, and Spirodela. Let’s start with Wolffia globosa which is used as a vegetable in Burma, Laos and Thailand. Its flavor is similar to sweet cabbage. Wolffia, which has the smallest blossom in the world, reproduces quickly making it a sustainable crop if the water is wholesome, which is a significant problem. In the wild, duckweeds tend to grow in poor water. Wolffia is 20% protein (more than soybeans) 44% carbohydrates, 5% fat has vitamins C, A, B6, and Niacin. Also called Khai-nam (eggs of the water) and Mijinko-uji-kusa, Wolffia is naturalized in California, Illinois, Kentucky, Tennessee and Florida. Unfortunately it is tiny, about 1/32 of an inch or the size of the eye of a needle. It’s a floating tiny disk with no root though it can have little hairs on its margin. It is so small it looks like meal floating on the water, hence its name watermeal. The tiniest and the tastiest. Best to raise your own in good water while keeping out lesser species.

Lemna minor

Lemna is much larger than Wolffia. It usually has three attached floating leaves (called fronds) and at least one vertical root root per frond. Lemna, also called water lentils, is typically less than a quarter inch wide, some species an eight of an inch wide. Dried Lemna is used as cattle feed having up to 45% protein, 4% fat. Unfortunately, from the human point of view, it is also high in calcium oxalate. To quote Missouri Botanical Garden (www.mobot.org)

“Calcium oxalate is not a nutrient (nor a beneficial source of calcium), and it can be toxic in large doses. Duckweeds can contain up to 2 — 4 percent oxalic acid equivalents by weight. However, oxalate also is found in a great many leafy and very nutritious vegetables, including spinach, swiss chard and others. In these edible vegetables, calcium oxalate is found in at levels up to 0.5 — 1 percent. So, minimizing oxalate has the potential to make duckweeds more nutritious and digestible.

However, published reports of calcium oxalate levels in duckweeds are likely to be misleading. The late Vincent Franceschi (Washington State University) demonstrated that the calcium oxalate content of Lemna minor depends greatly on the calcium content of the water on which they are growing. Elevated calcium in the water favors formation of calcium oxalate crystals, and their content can be lowered by growth on low-calcium medium. It seems likely that placing duckweed on soft water for a reasonably short period could lower oxalate content significantly in a practical setting…

Harvesting Wolffia in Thailand

For people to eat duckweed, it would need to be grown under sanitary conditions. In addition, it may be desirable to pay attention to the calcium content. Evidence is now emerging that the absorption of dietary oxalate makes a major contribution to urinary oxalate excretion, particularly in stone formers. There is a patent on a method to select duckweeds for human consumption.”

To all of that I would add that perhaps some experimenting is in order. Dry heat has been used to break down calcium oxalate in other foods, Jack In The Pulpit comes to mind. Sometimes moist heat works, as in taro. Cooking — boiling or roasting — would also kill any bacteria et cetera on or in the duckweed from the water (high nutrient water is often caused by… duck droppings.) A second option, as some suggest, is to boil the duckweed, change water, then blend it. There is a practical side to that as well. Pistia stratiotes seedlings look similar, grow in the same place and time, and are the same size. They must be cooked.

Spirodela, Giant Duckweed, is not edible.

Duckweeds are found in quiet, nutrient rich wetlands and ponds. They require high levels of nutrients to “bud” which means if a pond has a lot of duckweed the pond has excessive nutrients. Duckweed does not like moving water or windswept water even if the nutrients are high. Duckweeds bud. Under ideal conditions one duckweed frond can produce 17,500 “daughters” in just two weeks. With such high reproduction rate duckweed can cover the surface of ponds in just a few weeks. That is also why it is being considered for biodiesel because it has five to six times the amount of starch as corn. Duckweed also provides shelter for frogs, snakes, fish, insects and crustaceans. Grass Carp and Koi eat it. Perhaps the best way to to eat duckweed is to eat what eats it.

Sculling through duckweed

Giant Duckweed, Spirodela polyrhiza, was Lemna polyrhiza. There is one reference that says it has been used as food. Details are absent. I haven’t tried it. Giant Duckweed is frequently found growing in local rivers, ponds, lakes, and sloughs. In Florida, from the peninsula west to the central panhandle. It has two to three rounded leaves usually connected with each usually having several roots (up to nine) hanging beneath each leaf. The underleaf surface of Giant Duckweed is dark red. It can be easily confused with the exotic plant, Landoltia punctata. Landoltia duckweed is smaller than Spirodela polyrhiza, is more shoe-shaped, does not have a red dot on top, usually has only up to four roots, and sometimes has a red margin on the underneath of the leaves. It is spotted, as its name suggests.

Wolffia (WOLF-ee-ah or wolf-EE-ah) is named for Johann Friedrich Wolff, 18th century German botanist and physician. Spirodela (spear-row-DELL-ah) is from the Greek spira (spiral) and delos (clear), referring to spiral vessels clearly visible through the whole plant. Lemna (and various spellings) in Greek means port, which usually has quiet water. In fact, near my grandfather’s village in the Mani is a town called Lemeni. It’s at the end of a long, bay surrounded on three sides by huge mountains, and a cute hotel clinging to a cliff.

One last point: Frankly I think using an old swimming pool or the like to raise duckweed in would be the best. In natural ponds duckweed tends to collect detritus. A handful of duckweed includes a quarter handful of debris. It can be an aquaculture crop but it would take some planning.

PS: The leopard frog is edible.

Feed Your Livestock AND Your Family With Prolific, Fast-Growing Duckweed

Image source: Bioponica.net

As someone who raises livestock, I’m always interested in sourcing low-cost feed alternatives. Duckweed has been gaining a lot of attention in the farming community, owing to its ease of cultivation and the growing proof of its usefulness as a high-protein feed supplement.

Duckweed packs crude protein of 35 to 43 percent, fiber of 5 to 15 percent, polyunsaturated fat of 5 percent, and a host of trace minerals, calcium and Vitamins A and B. Its protein content is said to be equal to that of dried soybean meal. Not limited only to ducks, duckweed is fed to swine, chicken, cattle, sheep, goats, rabbits and farmed fish in many developing countries, with very positive results.

Duckweed is probably the smallest but fastest-growing plant there is. Grown in ideal conditions, it can double its weight in just 16-48 hours. Farmers who grow feed crops have found duckweed to be much more productive than soybean in terms of protein per surface area. It can produce 5-8 tons of dry matter for every acre per year, while soybeans produce less than a ton per acre each year depending on species, nutrient supply in the water, climate and environmental conditions.

Common duckweed, or lemna minor, grows in thick blanket-like mats on fresh or brackish still waters such as ponds, lagoons, swamps and slow-moving streams, especially those containing high amounts of nutrients like nitrogen and phosphorous. That’s why it’s often found in wastewater coming from residential areas, crop farms, hog and poultry operations, cattle feedlots, slaughterhouses and food processing plants, where effluent, excess fertilizers and slurry abound.

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According to a study by the UN’s Food and Agriculture Organization (FAO), duckweed acts as a nutrient sink — absorbing primarily nitrogen, phosphorus, calcium, sodium, potassium, magnesium, carbon and chloride from waste matter. Depending on the water source, duckweed may be used as an animal feed or fertilizer. It may have to be decontaminated, though, prior to feeding to animals if there is a presence of heavy metals, as these are also consumed by the duckweed.

ANIMAL FEED

Duckweed can provide all the protein needs of tilapia and carp — which is why it works great for aquaponics. It can either be fed fresh as the solitary feed, but a combination of 50 percent dried duckweed and commercial pellets or other feed components produces much better results. Duckweed can be grown separately and then given to the fish, or grown in the same pond or container. Other aquatic animals that benefit from fresh duckweed are catfish, snakehead, silver barb, milkfish, jade perch and crayfish.

For livestock, duckweed is best given dry. It is highly recommended for small-scale integrated farming operations that include fish, pigs, chickens, quails, rabbits and ducks. For poultry, dehydrated duckweed can replace up to 40 percent of conventional feeds of laying hens and older broilers. Feeding trials in Peru have demonstrated that duckweed can substitute for the soybean meal for layers and broilers. Duckweed-fed layers produced more eggs of the same or higher quality as control birds fed the formulated diets.

Duckweed is particularly noted for its high concentrations of K and P pigments, particularly carotene and xanthophylls — valued in poultry operations as these impart color to chicken skin and egg yolks.

For pigs, very little research has been done but a 30 percent dried duckweed diet was given to hogs in Vietnam and it resulted in high-nutrient digestibility.

HUMAN CONSUMPTION

But the best thing about duckweed is that it is also edible for humans. Duckweed resembles in taste to watercress or spinach. The wolffia genus has traditionally played a role in Asian cuisine, where it is used as a nutritious vegetable by the Thai, Burmese and Laotians. Duckweed can be mixed into soups and salad, or used in sandwiches as a substitute for alfalfa, lettuce, watercress or spinach.

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Duckweed is found all around the world. It survives in extreme temperatures except deserts and perennially frozen regions. It thrives best in tropical and subtropical zones, but can grow anywhere with temperatures between 63 degrees and 86 degrees F (or water temperatures between 42 and 91 degrees F). Some species tolerate winters by sinking and laying dormant at the bottom of the water, only to resurface during warmer weather when normal growth can resume. Depending on species, duckweed thrives in ph levels 5 to 9, but likes the 6.5 to 7.5 range best.

FARMING, INDUSTRIAL USE AND PROCESSING

Duckweed needs to be carefully managed, as it is notorious for invasiveness. It can take over a small pond in a matter of weeks if left unchecked. Once a colony covers a pond’s entire surface, it can block sunlight and deplete the oxygen underneath, suffocating fish and other submerged plant life. Duckweed should be harvested frequently, preferably daily.

Some natural, non-chemical measures you can use to prevent duckweed overgrowth are:

  • Raking and netting it often.
  • Aerating, or possibly putting a water fountain which creates some movement in the water surface.
  • Shading, which can be done by planting on the south side of the pond.
  • Placing in the pond weed-eating water birds such as ducks, coots and moorhens, as well as herbivorous and omnivorous fish like tilapia, carp and silver barb
  • Growing water lilies, lotuses and other plants with wide, floating leaves

Since duckweed contains up to 90-95 percent water, it is bulky and highly perishable when harvested. Collecting and dehydrating it on a large scale can be very cumbersome, time-consuming and expensive. The technology for desiccating duckweed on a massive scale has not yet been developed, so we can’t expect it to be commercially available in powder or pellet form anytime soon. For now, natural methods like sun-drying or drying in the shade with fans is more feasible for homesteaders and small farmers like you and me.

Have you ever used duckweed? What tips do you have? Share them in the section below:

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I have a confession to make. I really like duckweed. I think that it’s pretty, and can be really interesting to look at. The way that it propagates so rapidly is really impressive, and the free-floating roots are neat. Watermeal, a type of duckweed, doesn’t even have roots, it just absorbs nutrients and water directly through the bottom of it’s frond. Watermeal is also worth noting for being the smallest known flowering plant.

Duckweed, though, can be a huge problem in a pond. In good conditions, a duckweed plant can bud and divide once per day, meaning a daily doubling of the plant population and complete coverage of a large pond in weeks. Many pond owners have learned that duckweed can be an object lesson in the power of exponential growth. Coverage of a pond with duckweed and watermeal (they’re often found together) can cause significant problems for a pond. They block the sun’s light from penetrating the water, which will quickly kill off healthy, water-cleaning algae. Without this algae, nutrient levels will explode, creating unhealthy algae blooms and significant buildup of organic debris in the pond (the sludge layer). This will encourage growth of anaerobic bacteria, which create toxic water conditions that can kill fish, turtles, and other plants and further encourage the duckweed proliferation. That’s all bad.

Smaller backyard ponds generally don’t have much trouble with duckweed. That’s because it’s a fairly fragile plant that doesn’t do very well in moving water, and a pond with a fountain or waterfall will usually move enough to keep it down. It tends to be large ponds and even small lakes (especially manmade ones) that have the most trouble with duckweed. In a large, relatively stagnant pond, duckweed’s rapid proliferation and tendency to travel along waterways and on animals can cause it to take hold and completely take over a pond quickly, and once it’s got hold it can be difficult to get rid of. If you have a strategy, though, you can control unwanted infestations and even prevent it from taking hold.

Preventing and Controlling Duckweed

Eliminating established duckweed can be done with certain herbicidal chemicals, but this isn’t the route that I recommend, especially not at first. Rather, I’d go with a two-pronged mechanical approach to removing the pest. The first step is to simply skim out as much duckweed as you can. A simple pond net or even a pool skimmer or fine fishing net can be used. Wait to do it on a windy day, if possible, when the plants will be more compressed on one side of the pond. You’d be amazed at how quickly you can devastate the population of duckweed in your pond.

This won’t, however, be a permanent solution. If even a few tiny plants avoid removal, then they will likely come back, sometimes covering a pond in as little as a week. Once you’ve got the majority of the weeds out of the pond, though, you can go on to the second part of your attack, which will keep the duckweed from taking over again.

The same fragility that makes duckweed a rare problem in small ponds can be taken advantage of in larger ponds with one or both of two pieces of equipment. The first is a simple fountain, though a larger one than you would see in a small pond. Large pond fountains do two things: first, they agitate the water surface, making it more difficult for the duckweed to survive and spread. Second, it aerates the water, which will give the healthy aerobic algae a chance to remove some of the excess nutrients from the water that the duckweed thrives on.

The second simple piece of equipment that can help to eliminate duckweed infestations is a bubble aerator. This accomplishes the same tasks as the fountain, though it is far better at deep aeration and not as good at surface agitation. A good bubble aerator is just as, if not more, useful for keeping a pond healthy in a larger body of water, especially ponds that take in a lot of agricultural or commercial runoff that can carry huge amounts of nutrients that need lots of healthy algae to deal with.

Huge thanks to Joel, a customer who sent us an email telling us about his experience with getting rid of duckweed, along with the images that accompany this post!

Here are before and after pictures taken just one week apart. Our pond was completely covered by Duck Weed and Milweed. No fish or turtles any more. We installed the Kasko just over a week ago and skimmed the offending growth. Now it looks great and is remaining free of new growth. Aeration really works! We’ll soon be stocking with fish again! Thanks!

Duckweed and Watermeal Reduction

Oxygen is the most important constituent of a lake or pond’s health, as it’s an essential element for all aquatic organisms that breathe. Therefore, there is a direct relationship between the oxygen concentrations and exchanges occurring in a lake or pond, and the physiological status of aquatic organisms. Without oxygen at the bottom of a pond or lake, anaerobic bacteria (those that live without oxygen) produce an acid environment. These acids not only increase acidity but also cause a massive release of phosphorus and nitrogen, two major fertilizers, from the organic sediment into the water column of the pond or lake. These fertilizers feed duckweed and watermeal increasing their quantity and density.

Aeration systems are ideal for oxygenating a lake or pond that has been overtaken by duckweed or watermeal. By increasing dissolved oxygen in an environment depleted of oxygen, water quality improves and fish and other aquatic wildlife thrive. Aerobic bacteria thrive off increased oxygen levels, resulting in improved water quality and natural decomposition of organic matter—reducing duckweed and other plant life.

CLEAN-FLO’s approach to natural control involves the use of laminar flow aeration. Our aeration technology is proven to oxygenate the entire water column and the organic sediments that cover the bottom. The Clean-Flo process of water body restoration provides a custom solution for providing aeration in your water-body from bottom to top.

Duckweed can be quite problematic for pond owners as the aquatic plant lowers the oxygen levels of small ponds. The deprivation of oxygen kills fish, but can also cause problems with the good green algae found in non-moving waters.

To restore your pond and prevent further issues, you need to look into homemade duckweed killer. This invasive plant lives in nutrient-rich ponds alongside another problem water plant called watermeal. These two plants will work together to cover the entire body of water when the perfect conditions are met.

Whether you have these plants in your pond, control needs to start in early spring. Depending on the severity of the invasion, results can take several years to see.

How to Identify Duckweed

As the smallest flowering plants, free-floating duckweed, also known as Lemna minor, ranges in size from 1/16 inch to ¼ inch. Aside from its small size one of the most identifying traits of duckweed is that it floats on the water’s surface and does not attach itself to the bottom of the pond.

Having one to three leaves, duckweed has a very fine root hanging from the bottom of the plant to absorb nutrients. Not attached to anything, the plant is free to move about the water, whether it’s following currents or being blown along by the wind.

This invasive plant thrives in slow-moving or motionless bodies of water. Growing the plant does require a lot of nutrients with nitrogen and phosphorus high on the list. Nutrient sources for these plants come from a variety of sources, including tree leaves, leaky septic tanks or systems, runoff from farming, fertilizer, and Canada Geese.

Do I Need to Remove Duckweed?

Most of the time removing duckweed is a matter of personal choice. People have a love/hate relationship with it. For ponds with fish or other water plants, such as water lilies, these fast-growing ground cover plants can cause numerous problems.

Too much duckweed creates a spike in ammonia levels and reduces oxygen levels in the water. This causes issues for fish and affects the growth of your other water plants. As one of the most invasive plant species, at least for water, duckweed depletes oxygen because as it grows, some die off and beneficial bacteria must work to break down the decomposing plants, causing them to use more oxygen than usual.

If too much duckweed is dying, biological filtration is affected and results in the spike of ammonia and nitrites. These problems will continue to occur until the decaying waste has been removed.

Amazing DIY Duckweed Killer Ideas

1. Introduce Duckweed Predators

How to get rid of duckweed naturally involves using biological controls, which includes introducing natural predators like grass carp, goldfish, and koi. Introducing these predators to your entire pond and the surrounding area will control an already established overgrowth of the floating plant. This method is more to prevent growth in larger ponds or to keep a smaller problem under control.

2. Aquatic Herbicide

If the duckweed problem is out of control, you might need to use chemical herbicides to get a handle on it.

Recipe for Aquatic Herbicide

  • 3.2 fluid ounces aquatic herbicide (diquate as an active ingredient)
  • 10 gallons of water
  • A 1-ounce aquatic wetting agent

Use a large bucket to mix all three components. Pour the mixture into a pump sprayer. Do not spray the entire surface of the pond; only spray the plants with the aquatic herbicide. Too much reduces the oxygen in the water, which can harm your fish and other plants.

If the problem persists, repeat application in two weeks. Always use aquatic herbicide as a spot treatment, spraying the plants directly.

You can also mix chelated copper algaecide with the diluted aquatic herbicide for more effective results. The ratio would be 1 part copper to 2 parts herbicide.

Along with algae, duckweed grows in fountains. Fountain algae control with vinegar has been proven successful on algae growth, but the results are mixed with duckweed.

Vinegar can eliminate many aquatic weeds, and a fountain is a contained environment, so the vinegar will not harm other aquatic plants or life.

3. Preventive Measures

Learning how to get rid of duckweed requires learning about prevention. The safest and most effective homemade duckweed killer is to control it naturally. Taking care of the duckweed before it has time to spread prevents the need for chemical treatments, such as the aquatic herbicide.

One of the ways to prevent a duckweed infestation is through aeration. Aerating smaller ponds creates movement in otherwise still waters.

The bubble aeration deprives the plant of needed nutrients; the lower nutrient levels, the less chance the plant has to survive. Epsom salt uses in the garden include improving nutrient absorption in plants with no increased nutrients to ponds through runoff.

Leaf build up along the bottom of ponds encourages duckweed growth. Remove the dead leaves from pond water to prevent the black stinky ooze that feeds duckweed.

Once you clean up the leaves from the bottom, you need to find a way to avoid new leaves from accumulating on the pond’s surface for an effective duckweed control.

4. Manual Removal

One way to get rid of these tiny plants is through manually removing them. When manually removing the duckweed it is best to do it on a windy day, as the wind will push the plant along the edges of the pond surface making it easier to take out.

Use a pool skimmer net to scoop up the plants, or you can use a pool vacuum. Skim the water surface with the tool to scoop up the plants. This is also the best way to maintain your ponds, as it won’t harm your water plants or animals currently living in the pond.

While a weed killer using vinegar Epsom salt and Dawn isn’t going to be effective on duckweed because it is an aquatic plant, you can use this mixture on other weeds in your yard like crabgrass, Creeping Charlie and other pesky, invasive species.

Thank you for reading this post about duckweed. We hope some of these homemade duckweed killer ideas were helpful. If you found any of our tips on how to get rid of duckweed useful, please take a minute to these weed killer tips on Facebook and Pinterest.

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