Duckweed – a must have for Microponicists
Duckweed is one of the best-kept secrets of Urban Farming.
It is a high quality feedstuff that can be produced in useful quantities at little cost and with little effort. Of equal interest (particularly in an Aquaponics context) is its ability to remove nutrients from water.
We began growing duckweed in 2004. Initially, we used it to supplement the pelletised rations that we fed to our Japanese quail. In more recent times, it has become an important part of the diet that we provide to our Jade Perch.
In the right conditions, this tiny plant can double its mass every 24 – 48 hours. Close control of the production parameters for duckweed is relatively easy in the small ponds and tanks favoured by backyard food producers.
Its explosive growth rate enables you to harvest and feed fresh duckweed on a daily basis.
At 35% to 40%, it has a higher protein level than Soya beans and higher concentrations of the essential amino acids, lysine and methionine than most plant proteins.
The other great news is that growing duckweed is easy.
You can purchase your initial stocks from most aquarium supply shops…or from vendors on Ebay.
You can use any open tank, large tub or in-ground pond. Place smaller containers in semi-shade or somewhere that you are able to shelter them from the worst of the summer heat.
While it is not essential, recirculating water from your fish tank is desirable. Aside from saving you the effort of bucketing water from your fish tank, recirculating the water will ensure that the nutrient levels in your duckweed pond remain at a consistent level.
You should aim for complete and dense cover of duckweed (within the range 0.6kg/m2 – 1.2kg/m2) for backyard farming purposes. Much below this and algal blooms will be an issue and much above it will cause it to self-mulch. Wind or fast-flowing water will also cause diminished production due to self-mulching.
While a variety of organic materials can be used to supply nutrients for duckweed, the logical source for Aquaponicists is their fish tanks. Of particular importance to aquaponicists, is the plant’s nutritional preference for nitrogen in the form of ammonia.
Duckweed is capable of rapid growth in water containing trace elements of nutrients. Interestingly, we almost killed off a batch of duckweed through overdosing it with poultry manure.
Temperature and sunlight are more important growth parameters than nutrient concentrations.
Duckweed grows across a wide temperature range – between 6oC and 33oC – but we’ve determined that it grows best in a range of 18oC to 24oC. We know that growth slows progressively up to 30oC and the plant begins to die off quickly at around 33oC.
While it will live in pH 5 to 9, the optimum pH for growing duckweed is in the range of pH 6.5 to 7.5 – also the preferred range for aquaponics systems.
Feeding out duckweed is as simple as dragging a kitchen sieve through the duckweed tank and placing it into your fish tank.
To avoid the duckweed from being pumped out of the fish tank, we made up an inexpensive duckweed feeder from a bucket with the bottom removed. The bucket is suspended in the water and the duckweed is placed into the bucket. This arrangement allows the fish to access the duckweed without distributing it throughout the tank.
Jade perch waiting for duckweed.
Surplus duckweed can easily be dried and stored for later use. When drying small quantities, we allow the duckweed to drain in a kitchen sieve and then spread it thinly over several thicknesses of newspaper or kitchen towel. Turn it over several times each day for two or three days. Store it in an airtight plastic container.
Freezing is actually our preferred duckweed storage method. We simply gather up the tiny plants in a small kitchen sieve and squeeze the excess water out of them before arranging the mass in a shallow plastic container.
After freezing, we turn it out of the plastic mould and place the duckweed biscuit into a large storage container. Whenever we need duckweed for one of our fish, we select what we need from the storage container in the freezer and float it on the surface of the fish tank.
Frozen duckweed – fast food for fish.
To summarise, duckweed is a high quality source of plant protein that grows quickly, costs virtually nothing to produce and requires little labour. It offers the added benefit of being able to remove nutrients from water.
Our first challenge was to learn how to grow duckweed in consistent, predictable quantities.
Our current focus is on the full integration of the plant into an aquaponics system. We want to be able to grow duckweed to remove nutrients, feed fish and other small livestock and to conserve water through reduced evaporation.
Duckweed is a must have for Microponicists.
-o0o-
This article was first published in May 2009 and reviewed in October 2017.
I need to purchase some duckweed, do you know any outlets. I can buy on line, as I live up near Blackbutt. on the range.
I am looking for some watermeal to use as a food for my koi but I am having trouble getting ahold of any. Could anyone point me to where I might find some?
Thanks!
hey gary,
im just wondering if duck weed is ok to feed to frogs and if not what are some good native plants that are low and can feed both frogs and fish.at school wer building a frog pond and i need to find out wat is a good food sourch and any thing that is low so they can hide in
p.s. sorry to trouble u with my silly questions 🙂
thanks
shyanne
Shyanne Fitzpatrick…..I don’t know which frogs will eat duckweed but any frog will eat the other organisms that are attracted to (or sheltered by) the duckweed. Azolla is another aquatic plant that will live happily in your pond. Be aware that both duckweed and azolla will take over your pond if they are not harvested at very regular intervals.
the only interest i have with duckweed is if i can add this to my compost and maybe use as mulch around plants to inhebit the weeds. Any advice.
How do you dry the duckweed?
Alexandra…..The best way to dry duckweed depends on the amount you need. Small quantities can be dried by squeezing out as much water as possible and spreading the duckweed on newspaper or kitchen towel – turn it regularly. Large quantities have been dried by spreading it over the floor of a tunnel house and turning it regularly…..with a leaf blower.
We actually prefer to freeze it.
Please help me to find out how to get rid of duckweed its in our horses dam and they wont drink from it. Its covered in the stuff
What temp in F does the duckweed grow best ? Where can i find more info about growing it and azolla.
Can anyone identify a pest that has covered our house pond since all the rain this year?
It has a tiny green leaf and a large “beard like” growth of black fibre under the water.
Approx 1 cm long. It has choked the water lily growth and not sure how go remove it.
Thanks
Gary,
You mentioned using a basic aquarium setup with air, filtration and biofilter for home duckweed production. How important is it to have these conditions compared to a tub/drum with regular water changes when growing duckweed. Does duckweed need air in the water? Does it benifit from the biofiltration? Any additional info would be helpful.
thanks,
Scott
Garry, you mentioned that you use your duckweed with Black Soldier Flies. How do you feed them? Do you give it to them dried or fresh. Also, does it attract the Mama fly or do you need other foods to do that. I have a BSFL bin going for my food scraps that I feed to my catfish and I am looking for ways to increase my BSFL fly production using the byproducts of my catfish. (I was also considering using azolla for the BSFL — have you done that) Is the duckweed a complete meal for the BSFL? Could you enlighten me as much as you can on duckweed and BSFL 🙂
Thanks, Tim
Timothy West…….We often just mix the duckweed up with BSF larvae when we’re feeding chickens or ducks. We refer to this as a chicken salad – from the chicken’s perspective.
Duckweed is overwhelming water so leaving it to drain well is a useful thing to do. You can also dry it and incorporate it into poultry rations.
I’m not a huge fan of Azolla – I just prefer duckweed.
I feed duckweed to BSF larvae so I suppose that they would also eat Azolla. As to whether it’s a complete meal or not, why don’t you trial it.
You can get plenty of information on both duckweed and BSFL on my Aquaponics HQ forum.
How to get rid of duckweek (large leaf style) from dam? I don’t want it and would like to eliminate it from my medium size dam. Can anyone help?
Sue Crichton…….I responded to a similar question earlier in these comments.
Gary,
I’m curious about duckweed and azolla. I’ve looked around online and found that both are considered good livestock rations, though I’ve noticed that azolla is considered great for dairy animals, while duckweed leans more towards poultry, pigs, rabbits, and fish. Considering that Azolla has nitrogen-fixing abilities w/ anaebaena algae, making it similar to things like alfalfa hay, perhaps this makes it more suitable to ruminants like goats and cattle? I’m not sure which source to trust, as I get the impression that azolla and duckweed growers are competing with each other over who has the superior aquatic plant. Do you think that one could use the azolla in a vermiponics system, burying a handful of it in a media bed to allow for nitrogen to be supplied to some lettuces, or even a separate duckweed tank (phosphorus being the limiting factor)? Are there any prevailing advantages that duckweed has over azolla to make it more worthwhile?
Thanks,
Mike
Mike…..I suggest that any preference for Azolla for dairy animals might be because it’s a larger plant than duckweed and would be a more satisfying mouthful for larger livestock. Duckweed on the other hand lends itself to fish and micro-livestock.
I can see no reason why you couldn’t use azolla in a vermiponics system. While organic matter passes through worms, their main diet is bacteria and other microscopic organisms. As the azolla begins to decompose, the worms would like come in search of food. Give it a try.
I’ve grown both azolla and duckweed but I try to keep them separate because, in my experience, azolla quickly overwhelms the duckweed. When I grow duckweed, I like to freeze it in trays. I then break the frozen duckweed into pieces which I then feed to my fish. Freezing the duckweed allows me to feed it out with much less mess in the tank. The fish chase the frozen chunks around the tank eating the duckweed as it thaws.
Hi Gary, I have been greatly shocked by the rapid coverage of what I have just found out to be duck weed over our dam. The dam is about 3 meters deep 100ft width and although it is at it’s highest level for 10 years and appeared in good shape it now smells stagnant. My husband wants to stock it with fish but my concern is that the fingerlings wont survive. I was also using the dam as a water source for horses but they won’t drink from it anymore. Can you suggest a fish that might survive: I noticed you mentioned perch. Can you suggest a way to erradicate this or control the growth as mechanical removal is not possible.
Trish……if duckweed is thriving in your dam, it’s because there’s a nutrient source present. This may be nothing more than runoff containing some animal manures.
Essentially, there are three ways to contro duckweed…..chemical, biological and mechanical.
Chemical – I’m not sure what herbicides could be used to control the plant since I spend more time encouraging it (in my backyard) that attempting to get rid of it. Your local agriculture extension officer may be able to advise you. If you google “control of duckweed” you’ll see that there are lots of herbicides that are claimed to kill the plant…..although it seems to be a long term job. My concern about the chemical option is the impact on other organisms. In any case, it seems that you will need to poison the weed over several seasons if you are going to eradicate it using this method.
Biological – You will need to remove the nutrient source by restricting livestock access to the dam and the run-off area that feeds it. The presence of duckweed in large numbers is the consequence of nutrient availability…..you have to cut the food supply. While it would be good to find a fish species that will eat it (and that depends on where you live anyway) it’s unlikely that they will keep up with the growth of the plant…..particularly since the fish will begin to provide even more nutrients.
The fish solution is likely to become effective only once you get some control over it in the first place.
Mechanical– This involves physical removal of the plant. While this may not be what you want to hear, my own approach would be (since you already have the problem) to attempt to see it as an opportunity rather than a problem.
When you refer to mechanical removal not being possible, what exactly do you mean? Is it the shape of your dam…..or simply the scope of the task?
If you could find a way to harvest it, you could feed it to livestock (cattle, pigs, chickens, ducks) or make compost from it, or feed a bio-digester…..or use it as a green mulch…..or other things.
Mechanical harvesting will never get rid of the plant entirely but it will allow you to get it under control to the point where other options (including stocking the dam with fish) become possible……and, if you could find a good use for the plant, you may reach the point where you no longer see it as a pest but rather as a resource.
Your dam will become a far more valuable resource if you can take an integrated approach to its management.
I hope this has been of help. Please come back if you need clarification on anything I’ve written and let me know how you got on anyway.
Do you sell duckweed? Or can you tell me how to grow it in an aquarium for human consumption? My daughter has vitiligo, white spots on the body, and duckweed is one of the best natural remedies for the ailment. I haven’t been able to find any organic here where I live…any suggestions?
Susan…….I don’t sell duckweed……but it is a very common plant. It’s often to be found in aquarium or pond shops. Where are you located? I might be able to direct you to Aquaponics HQ forum members who are near you and might have some if you can’t locate it.
Growing duckweed is very easy. You could use an organic hydroponic nutrient to ensure that the duckweed is clean (important given its proposed use)……and a very basic aquarium system managed to provide the optimum growing conditions for the duckweed. I’d suggest a small air pump, a very basic mechanical filter and a simply moving bed bio-filter.
Feel free to contact me if you need further detail around this.
While I’m aware that some Thai tribespeople eat duckweed as a food, I’m intrigued at your suggestion that it is used for medicinal purposes……I’ve never heard about that before. Can you connect me with more information about it?
Hi Gary
Are you discussing the native Duckweed plant
If not, does the native variety have the same qualities as other varieties, do you sell the native variety and which fish eat it.
My dam is full of Gudgeons ( a pest) but i am introducing native fish to eat them but am happy for the gudgeons ( guppys) to fatten up on the Duckweed
steveuwa……there are several species of duckweed that are native to Australia. Some of the leading researchers around duckweed are also Australian. There was even a Duckweed research centre based at the University of New England at Armidale in New South Wales.
Jade perch happily eat duckweed and silver perch can be trained to eat it, too.
I don’t sell duckweed but I’d be very surprised if you had much trouble finding some……it’s often available through aquarium shops.
Hey Gary!!!
I’m doing an assignment for a Biology course I’m doing and came across your site on Google. The questions and answers that are listed upon this site have been considerately helpful in some of my “distant” questions. You seem to know alot about DUCKWEED, and I was wondering, what the basis of Duckweed is?
Like, the can control the aglae population, but how do they do this? why do they do this?
How come they are eaten by ducks and called “Duckweed” anyways?
Amanda……if you Google “duckweed” you will find volumes of information about this amazing plant.
Duckweed controls algae by denying it sunlight and nutrients. As to why duckweed controls algae…..it’s probably a natural occurrence rather than a conscious decision.
Duckweed’s taxonomical family name is Lemnaceae but it probably came to be called duckweed because ducks were seen eating it.
Gary,
My friend went to a lake and found what we hope is a duckweed.It has the size of a duckweed, the leave is 2-3 mm, but unlike what I saw in Wikipedia, the leaves actually are held together or stick together and it has some roots. I have taken pictures of it, can I somehow forward it to you and see if you can confirm that it is a duckweed. It is very small.
Many thanks
Janto
Janto…….there are many species of duckweed. It’s also possible that what you have is Azolla.
My experience suggests that those fish that will eat aquatic plants prefer duckweed. Duckweed is also easier to dry and handle.
You need to make sure that what your friend has is actually duckweed because, once you introduce it into your pond, you may have difficulty getting rid of it.
Gary, I am trying to grow duckweed and appreciate if you could help me. I have got a pond and am not sure if there is enough nutrient to grow duckweed. I have a fish farm and everyday twice or thrice, I would get rid of the sludge/fish waste. Should/Could I use this slude/waste as nutrient? how about dead fish? Just thinking how I could use the unwanted/dead fish as nutrient or fertilizer.
Thank you.
Janto
Janto……you could certainly use the sludge and solid waste from your fish farm as a nutrient source for duckweed.
The best way to do it would be to set up a simple batch aerobic digester arrangement. That way, you could mineralise the solids and add the nutrient-rich liquor to your pond (without the sludge). Email me if you need further guidance on how to set this up.
Dead or unwanted fish could be minced up and become a high protein part of the ration for poultry or pigs. I think this would be a much better use of the resource.
Thanks Gary, I can see they are all good reasons why it would be impractical.
Another reason might be this:
” Duckweeds can be grown separately and then provided to the fish, or produced in the same pond. Production of Lemna in the same pond is not likely to work efficiently, however. Vigorous aeration of the water, as is practiced in catfish-culture, will disturb the growth of the plant. The photosynthetic activities of the plant do not oxygenate the water, in fact the covering plants reduce gas-exchange with the atmosphere ”
http://www.mobot.org/jwcross/duckweed/Fish.htm
I initially just thought it might be simple and cheap, to have one pond, with the fish and their feed (duckweed) growing together. But I suppose that is just like a wild natural pond, and wouldn’t be highly productive.
John……Ponds can be enormously productive but they are generally much larger in area (and much more environmentally diverse) than the small aquaponics fish tanks that are in general use.
The fact that not all ideas are good ones should never stop one from generating them. Straying up the occasional dry gully is part of being innovative.
Having duckweed in a media-based system has lots going for it. It can be a valuable food supplement for some fish species and it has a useful role to play in maximising water quality.
We’ve also used is as a feedstock for our Black Soldier fly larvae and even as green mulch for our pot plants.
Its probably a stupid question, but why couldn’t you grow the duckweed in the fish tank ?
And if it is because the fish eat it, faster than it grows, would it be practical to protect some of the duckweed, with mesh underneath ?
It just that, I thought the duckweed would be good shade for the fish, and also remove excess nutrient, directly from the fish tank.
regards John
John…….It’s certainly not a stupid question but there are a few reasons for why it might not happen.
Duckweed will grow faster than the fish can eat it….so that’s not an issue………but, while fish will appreciate the shade cover, it becomes much more difficult to observe the fish and monitor their well-being.
In a media-based grow bed system, the duckweed will get picked up by the pumps and deposited in the grow beds (adding to the solids loading in the beds).
Duckweed can be grown in the same water column (check out The Queenslander) but in a separate grow tank.
In a raft system, duckweed shouldn’t be grown at all because it will end up in the grow tanks and make an awful mess. The plant is so prolific that, in the ideal conditions in a raft tank, even a single plant will grow to become millions in a very short time.
Hi Gary,
I’ve been avidly reading the article you wrote for Easy Aquaponics and wanted to let you know that I appreciate all the information you’ve given in a way that I can understand. I am interested in starting an aquaponics garden and am gathering as much info as I can. Thankyou for your wisdom and experience.
sal
sally……….and thank you for your kind words.
Hi,
I’m just on this website to find out what Duckweed eats and what climate does it prefer for a homework task. Do you think you would know?
Thanks,
Lauren
P.S This website is really cool!!!!!!
Lauren………duckweed prefers 18 – 24 degrees C and a pH of 6.5 to 7.5. It needs to be sheltered from strong winds. It only requires modest quantities of nutrients. It is interesting for its ability to feed on un-ionised ammonia.
A good cover of duckweed on the surface of the water will help to avoid algae growth but if it becomes too thick it will begin to self-much. The idea is to harvest it regularly but always leave enough to achieve a complete cover.
Hello again Gary, have been enjoying your, resently purchased, Aquaponics Manual. I was reading about the production of duckweed in its own grow bed & came across the challenge of slowing up the by product of mozzy larve. I was wondering if you could put afew fingerlings in the grow bed to clean up the mozzy larve & afew yabbies in, to clean up the the fish poo without upsetting the filtering effect of the duckweed.Also,have you any info about how long the native fish feed on mossy larve before they change their diet to more substancial fish foods? I dont want to put inedible fish in my aquaponic tanks !!! [ when I eventually started ] Regards Steve
Steve…..I’m pleased you liked The Urban Aquaponics Manual.
You can use fingerlings in the duckweed tank to control mosquito larvae – but be careful that the water temperature in the bed does not get too high.
As far as cleaning up the sediment, I suggest that you simply harvest all of the duckweed and vacuum the sediment out of the grow tank. Your non-aquaponic gardens will love it. Replace the duckweed when you’ve finished. We find that it takes very little time to do this task and it keeps the duckweed tank nice and clean…..and your fish tank water at optimum quality.