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.

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{ 42 comments… read them below or add one }

Engineering Student December 7, 2016 at 13:34

Hello!
I’m an engineering student designing a hydroponics system for a class project. I read about the Wolffia the other day, and would like to use it in my system. However, I am unable to find it for sale online. Does anyone know where I might be able to buy some to test?

Thanks!

Located in Oregon, USA

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Michael Reynolds April 7, 2016 at 06:50

Hello,

Great stuff – both the site and the duckweed.

What is approximate calorie count of dry weight duckweed?

Best wishes

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Max April 8, 2016 at 22:50

Hia, high school studen- am doing research on this… It’s bioethanol not diseal, for 100g of duckweed has 89calories

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Anne-Marie February 4, 2016 at 12:06

Where can I buy Duckweed in South Africa? Want to grow it for my ducks and chickens.

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Christia January 18, 2016 at 03:23

Thank-you; most helpful article. I am staying in South Africa and my pond is covered with Lemna, which is a major invasive species in our climate. I keep this pond especially for frogs and have various species of tadpoles throughout the year. How do I remove the duckwheat without killing off the tadpoles? Even if I physically try to remove it, tadpoles are entwined in the duckweed.

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Green Deane January 18, 2016 at 14:31

Wait until they grow up is one solution. Another is to feed them. They will learn to go to a spot for feeding just as fish do.

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Joseph L Morehouse May 22, 2015 at 23:59

I have been growing Duck weed for the last 5 years and eating it for 4 and it is a good food source during the summer at it to soups , breads,add to salads- make pesto out of it tasted great.

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Green Deane May 23, 2015 at 18:34

Got a botanical name so we can identify the “duckweed?”

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Carleton December 17, 2014 at 21:53

I am trying to grow duckweed. It has not been as easy as I had expected. I am trying to cover a 5 acre pond. I have had several problems. Wind / wave action on a slopped bank, hard freezes and low water to name a few. I would like to know what is the ideal fertilization . All nitrogen? 13.13.13? if known, I would like to know the optimal parts per million of what duckweed likes. Or at least a push in the right direction. This article has been very helpful and probably the best I have seen so far. I found the article from your first sentence Do ducks eat duckweed. My experience with that is , Yes and wild one too. Although , I would say the only two ducks that seem to pass other food up to feed on it are the Gadwalls and a Northern Shoveler. I also would guess that could be a local observation also. Maybe they like it more than the food that is available in my area but maybe not in another.

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max September 10, 2015 at 22:33

duckweed normal grows in a high concentration of nitrogen fertilizer IE wet lands
use as much as possible
its like a algea bloom

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Apollo Pampallis August 16, 2016 at 01:34

Dont chuck fertilizers in the water!!!! Bad enough contaminating the land with them and destroying the soil ecology before running into streams and subterranean aquifers!
Whats the point of eutrophying the water ecosystem and poisoning it just to grow the duckweed which tries to clean it? !!!

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Apollo Pampallis August 16, 2016 at 01:39

thanks for that! Just one minor detail ; delos means ‘reveal’ or ‘declare’ (Δήλος-where Apollo was born/revealed, δηλόνω-I reveal/declare, δήλοση-declaration), psyche-delic=reveals the soul

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Daniel Franks November 25, 2014 at 02:36

I really like this article and thank you for sharing it. I have bookmarked it and pinned it several times and only today responding! I am now researching food nutrition testing as I am an avid hydro and aquaponics grower and interested in how the nutritional values, especially calcium oxalate can be adjusted.

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Perry Calton September 25, 2014 at 20:57

I would like to connect with others with information about commercial use of duckweed.

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Colleen July 12, 2015 at 12:11

I want to grow it for food consumption. Im thinking I can, in a large aquarium. DW is high in the amino acid, lysine. I want to drink DW smoothies. Its interesting how it cleans polluted bodies of water and uptakes nutrients in the water. Check-out Heiner Freuhauf, .Classical Chinese Physician. He’s the person who said in lecture I attended…”if you want to study an interesting plant regarding health, look into duckweed- Wolfia. 🙂

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max September 10, 2015 at 22:33

how can I help? email -maxthezurviver@gmail

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Perry Calton September 20, 2014 at 21:01

Old website but still up needing updating.

I’m in SW Oklahoma and have water from Tom Steed Lake. It is very high in N and P and has green Algae.
I started researching crops that would grow using this water and learned of Duckweed. Supposedly DW will thrive in the water as evidenced by local ponds with green tops and farmers who cuss it.
I’m not a farmer but would be willing to consider it. OSU Extension is unfamiliar with any commercial use and is only aware of people who want to get rid of it. I learned that the Duckweed blocks sunlight and can kill the algae. That frogs love DW and some fish. That some DW is edible for humans and livestock. That the DW can be skimmed dried for compost. So, it seems that the problem with the water has opened the door for some commercial use.
I’m reaching out for anyone that could provide input. I like the idea of using what is considered polluted water that could be filtered with DW create multiple products at the same time.

Thanks, Perry

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Scott Smith April 9, 2015 at 20:43

Hello Perry, I feed it to my tilapia in my aquaponics systems. My vegetables are very happy, so are the tilapia. My big koi ponds are covered with DW, water very clean. It used to be terrible like pea soup every year, spent a fortune battling algae. Since I put DW in there, the koi eat it, and the water is crystal clean. It wont grow in my big tilapia pond because they wipe it out, so I constantly put the excess in there to feed them, and I’ve had them get five pounds easy in a year, then in the freezer they go. So yes, using it in fish farming and aquaponics has been very beneficial for me. Hopefully helpful.

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max September 10, 2015 at 22:36

in the winter, duckweed builds up starches and lays on the bottom of the pond- how bad was the freeze its use to warmer climates

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Tina June 13, 2014 at 08:58

I have an oversupply of duckweed in my pond. Clearing it weekly really is a very laborious task. Is there a way, chemically or biologically of eliminating this weed please?

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Mercer House May 27, 2014 at 09:20

I have so much Duckweed I can’t see straight! It has been a pain in my pond for over 20 years. It multiplies as much as six time per day in mid-summer. I also have plenty of turtles that if they eat it, it never seems to make a difference.

Invasive is an understatement! You can’t kill it or filter it or even net the stuff…

I even put Koi in the pond hoping to finally see the water, but to no avail. I would strongly suggest no one buy Duckweed, just stop by our vineyards and take all you can carry.

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mike May 28, 2014 at 10:01

You may (or may not) have some luck with grass carp in your pond. Grass carp are herbivorous and most suppliers sell only sterile grass carp. This avoids possible overpopulation and eliminates the threat if they should somehow get loose into the environment.

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Scott Smith April 9, 2015 at 20:22

Tilapia love it. Feed it to my babies everyday. I’ve had them clear the pond of it, they are pigs.

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Kelley August 1, 2016 at 20:30

We are using Grass Carp, they are sterile and seems to be helping. But still we are looking for something a little faster

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shaunamom May 24, 2014 at 16:55

Has anyone heard anything on the most efficient ways to CLEAN the duckweed of other contaminants…like dead bugs or small pieces of grass or leaves that have fallen into the water? We’re growing some now, but I haven’t thought of a way to do it that didn’t involve somewhat laborious picking out of the insects and such. :-/

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Green Deane May 24, 2014 at 17:40

Feed it to ducks (and chickens) then eat them.

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Tamra February 19, 2014 at 21:38

Great article! I grow duckweed commercially for various end products, including pet foods. The limiting factor for growing duckweed is usually nitrogen. It prefers ammonium over ammonia, so keep your pH at or just below 7.

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Vikki November 3, 2013 at 15:40

I have tons of Wolffia on my pond. Every summer it looks more like very green land instead of the pond it is. We feed it to our chickens and our ducks don’t mind it, but prefer more leafy greens.

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sloan drake August 19, 2013 at 02:11

Aquarium supply or pond supply. Most nurseries with aquatics as well. It does a great job filtering nitrates in my aquarium so composting or top dressing your plants should release it and benefit your plants greatly if your koi don’t swallow em all up first. Found em on internet before too but ran into issues with it being considered invasive.

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Josh August 12, 2013 at 13:35

I’m looking for some Wolffia but I can’t seem to find any anywhere. Does anyone know where I can find some?

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Kristina August 21, 2013 at 23:34

I have tons of duckweed, ordered it from Carolina Biological in May for student projects. I have it in the projects and several aquariums. It grows incredibly fast once you figure out what it needs. I use an aquarium fertilizer called Flourish. I have to skim it out of my tanks regularly as it grows so fast. It will not grow in my goldfish tank, so I put the excess in there for them to eat. I don’t think I’ll ever have to order it again!!

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Rebecca April 3, 2013 at 22:37

Do you know how much iron duckweed has in it?

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Marcus Banana February 19, 2013 at 16:18

Excellent Article!

Gonna keep this in mind… maybe make a just-duckweed tank for my aquaculture setup. I’m thinking…maybe… that with Wolffia’s high carb and protein content, and small size, this might be a good substitute for your typical ‘small, round, starchy staple’ for non-starch-eaters.

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vishal patel February 18, 2013 at 03:50

is it necessary to grow duckweed into pond water where it taken ?
what is the main nutrient element which will be required for the growth of duckweed?

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Green Deane February 18, 2013 at 08:04

No, but it needs what most plants need, good water, some fertilizer.

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Marthe Olesh August 22, 2012 at 14:12

Would rose of sharon seeds be starchy? And are albizzia julibrissin seeds eatable?

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Green Deane August 27, 2012 at 14:15

Seeds usually are starchy. As for the A. julibrissin seeds that’s debatable. Right now I fall on no.

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Tim Anderson April 17, 2012 at 13:30

i wonder if duck weed would make a good compost/fertilizer?

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Geoff Wane January 8, 2013 at 21:13

In reply to Tim,
I regularly skim my pond in an effort to thin the duck weed. I then use it as a green mulch around mainly palm trees and bushes in my yard. They seem to benefit a great deal from this.

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Keith March 18, 2015 at 10:39

Great way to remove excess nutrients from your pond that collects nutrients from run off.

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Keith March 18, 2015 at 10:36

You want to grow duck weed in nutrient rich water only to compost, and then feed to your plants? That doesn’t seem like it would make sense if you just feed the nutrient rich water to the the plants.

If one were to grow duckweed, it might be better to feed it to fish who could use the energy in the lipids, proteins, and carbohydrates for the fishes growth, and the fishes affluent to feed your ground plants.

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Apollo Pampallis August 16, 2016 at 01:43

I agree Keith, except if you are a vegetarian and dont want fish, but then again, if you are a vegetatian you may want to eat the duckweed for its high protein content, higher than just about any other green

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