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Duckweed Growing Tips and Tricks

March 7, 2012

I’ve been saying all along how easy it is to grow mega crops of duckweed, IF you know the tricks!

Duckweed grows on benign neglect in the wild. However, to cultivate it in a garden setting, duckweed does have a few definite needs if it is to thrive consistently.

1. Like any vascular plant, duckweed needs a minimum of nitrogen, phosphorus, potash and micro nutrients. Sources can be as simple as a little humus and/or soil or compost tea. To achieve high protein levels of 40% or greater, duckweed needs added nitrogen, preferably in the form of ammonia from animal waste. This is why it thrives so well in fish aquariums.

Nitrogen sources can include fish wastewater, chicken coop drainage, some types of grey water, vermiculture liquor, or aged manure. If a solid, place in a gunny sack and lower into the water column. This releases a steady amount of nitrogen and trace elements for a couple of weeks. Replace if you see duckweed roots grow to an inch or longer. Some people will occasionally spray the duckweed with an organic-based foliar spray as another source of nutrients.

2. Duckweed thrives at a pH of 6.0 to 7.5  If algae is present in large quantities, it can raise the pH to dangerous levels by virtue of CO2 production at night. The trick is to monitor pH, especially if algae is present. Treat pH extremes as described in my prior post. Encourage an adequate surface covering of duckweed at all times to suppress algae production.

3. Harvest duckweed as needed but leave about 1 1/2 to 2 pounds of wet duckweed per square meter on the surface of a pond daily. This insures enough of a cover to slow down algae growth or suppress it altogether. As an added benefit, this much covering also helps with mosquito control, water evaporation and temperature issues. More than 2 1/2 pounds of wet duckweed per square meter will result in its demise, as it self mulches at that concentration.

4. Duckweed prefers water temperatures of 50 to 90 degrees. Above or below that range, duckweed just sort of sits there. Much above 90 degrees, your duckweed crop will crash and it won’t be pretty. Ways to circumvent this is light shading from surrounding trees, plants or shade cloth hung over the growing area.

5. Keep water movement to a minimum. As duckweed floats on the surface, any strong wind will push it to the edge of the pond where it will begin to pile up in layers, effectively self-mulching the layers beneath. Grow taller food crops around the perimeter to shield it from the wind.

Duckweed is an amazing crop that gives much more than it gets, but still needs a few basic “gotta haves” in order to reach its full potential in a garden setting.

61 Comments leave one →
  1. Bonnie View, Port ,Antonio, JAMAICA permalink
    March 27, 2022 9:29 pm

    , Tamraf, your blog is superb in so many intriguing and useful ways. I wish that I had encountered it and you a decade ago! THANKS!!


  2. Sarah permalink
    August 9, 2021 6:55 am

    Ive killed off all weeds in a 20 meter garden…now I have an infestation of Common Duckweed with No pond!!! Will roundup kill it off?


    • August 9, 2021 8:06 am

      Normally duckweed grows on water. I have seen it grow on mud but to overtake a dry soil is nigh to impossible. Please post a pic and maybe we can help you ID the plant.


  3. April 26, 2021 1:48 pm

    I have seen fish successfully be raised in the same pond as duckweed but the duckweed needs to be netted off to one area and maintained. The problem that arises is that the fish eat the duckweed faster than it established. blushed.


  4. Carole L Groves permalink
    April 25, 2021 7:43 pm

    I am perplexed. Many states, as I recall, do not want Duckweed because it is invasive and difficult to get rid of. Will frost and snow kill duckweed (Michigan,zone 4). I just told my son that I planned to order Duckweed, and he asked why I would do that with an invasive plant. So, I see many surprising good facts, but do not want to clog natural ponds, lakes and rivers. Even in my own pond that I am rehabilitating, is there a way to plant to contain?


    • April 26, 2021 1:44 pm

      Dear Carol, two states ban importing duckweed, maybe one is two others since I last checked. I do not recommend replanting it in existing natural ponds or waterways in amy state. Rather, grow it in controlled man-made ponds with no spillover possible to natural waterways.


  5. Fransu permalink
    September 6, 2020 1:23 pm

    Hi, what is the ideal composition for a mixture to get the optimal duckweed growth rate?
    Thank you


  6. Yasin permalink
    August 29, 2020 11:15 pm

    Hello Tamra, i ve started to read this informative blog of yours. Thanks for it! Two queastions on this topi: Does manure need to be aged? And as i read somewhere else they were calculating yield 100 g/m2 but you say the yield as 1,5-2 pounds (700-900 g) per m2 here?


  7. Lajos Balogh permalink
    July 26, 2017 2:37 pm

    Every animal can eat duckweed on a farm? If not, then what animals can?


    • July 26, 2017 5:00 pm

      Dear Lajos, documented animals that eat duckweed include cattle, swine, chickens, ducks, rabbits, goats, and fish.


  8. Xilin permalink
    January 13, 2017 12:36 pm

    I just ordered some duckweed from Amazon to cover the pond surface to slow down water evaporation and feed my chickens and ducks. I live in East Bay area (45 minutes drive from San Francisco). There is one or couple of days frost every winter. My question is: Will the duckweed survive in the pond in winter? If not, what can I do to preserve some for regeneration during the cold winter days?


    • January 13, 2017 5:43 pm

      Depending on the species, some will form starchy “turions” and sink to the bottom of your pond to overwinter.
      In Kentucky, it takes several hard freezes for my species to totally dissapear. They do come back every spring. If worried, you can throw a mini greenhouse tent over a small kiddy pool and give your duckweed more warmth. I can extend my growing season another 6 weeks that way, albeit with reduced growth

      Liked by 1 person

  9. July 10, 2016 8:13 pm

    Thank you for such a helpful article. The problem I am encountering here is dosage. With ground plants, there’s always instructions of how many lbs of fertilizer per 100(example) square feet or so, and at what depth it should be tilled in etc…

    But with aquatics, that information is sorely lacking. For example, you show duckweed grown in totes. Maybe 20gallon size? How much fertilizer did you add to each?

    With the gunny sack method, how much solids to add? A shovelful maybe? But to how much water, so one doesn’t risk overfertilizing….A 20gal tote like you show, or a 2000gal pond since you mention water columns? That sounds deep. Such information would be very much appreciated. Thanks!


    • January 13, 2017 5:37 pm

      I go with organic fertilizer whenever possible aka manure. Dosage IS variable given your water quality, age and moisture content of manure, etc… I try out various increments of new sources of manure in small containers of the same water and add equal parts of duckweed to each. Give it a ten days to see which concentration works the best. Do add a bit of garden soil for micronutrients to each container along with one container just water and garden soil. (Control) Just insure that no herbicides have been used or leached into the aninal’s feed or your garden soil. Good luck!


  10. Anonymous permalink
    April 20, 2016 11:23 pm

    I just started to grow duckweed in my water container garden and some plastic bins. I am growing duckweed for a completely different purpose, clean the water for my carnivorous plants. The carnivorous plants like water lower than 150 TDS and my tap water here is around 250 TDS.


  11. Scott Bx permalink
    February 18, 2016 9:48 pm

    In Louisiana this stuff is a crazy plentiful and a pain in the butt. Why would someone want to grow it? Help me out and to understand.


    • February 18, 2016 10:20 pm

      LOL. Scott, the protein content rivals soy beans with better amino acid profile. It can outproduce soy ten to one. It is not GMO, and can tolerate a wide range of nutrient loads. It can be fed fresh to fish and ducks, or as a supplement to poultry, swine, or ruminants. Dried, all of the above can use it in even higher percentages. It’ll clean wastewater very effectively and the resulting biomass can be used as a green mulch. Purposely-grown duckweed can be processed for a wide variety of end products in animal or human food, bioplastics, biopharma, the list goes on and on. It’s as close to animal meat as we have in the plant kingdom. Next time you see a wild pond of duckweed, you can think, “WOW, who would have thought!”

      Liked by 1 person

    • Anonymous permalink
      July 10, 2016 12:59 pm

      I have just started farming fish and have high nutrient levels which cause algae to take over. When the algae dies it can deplete oxygen levels causing the fish to die. Duckweed is a way of keeping the nutrient levels under control.


  12. August 20, 2015 2:55 pm

    I just set up a 16 half barrel aquaponics with 10lbs of fish in 800 gal tank and 200 gal grow beds, one week in operation and things are proceeding great ,except for one thing APHIDS !! WHAT CAN i DO HELP STARTING SOME EXPERIMENTS WITH Bt then will move on to …..?


    • February 18, 2016 10:22 pm

      Michael, still have the problem? Let’s talk.


      • Jeremiah permalink
        February 25, 2016 11:30 am

        So what was the cure, I also just had an explosion of aphids.


    • February 25, 2016 10:07 pm

      Aphids- only thing I know to do is spray the mat a couple times a day and dunk em good. They do not like the movement or splashing. Plus, a good portion of them will simply die.


  13. July 3, 2014 9:50 am

    You can certainly see your enthusiasm in the work you write.
    The world hopes for even more passionate writers like
    you who aren’t afraid to mention how they believe.
    All the time follow your heart.


  14. Lorie permalink
    May 8, 2014 11:39 am

    Is there a specific article on drying & burning Duckweed to repel mosquitoes? Do you have any varieties for sale? I love your website and hope to introduce Duckweed usage to the local county extension office as a water purifier and mosquito repellant crop. Thank you !


    • February 25, 2016 10:20 pm

      I have burned dried duckweed in a citronella sort of way and frankly, it did not repel insects. Repelled ME with the smoke. 🙂 The mosquito reducer properties are theorized to be some trace molecule that they emit in water. It kills a certain kind of mosquito larvae, but not all species, unfortunately. Please do share your success story with your count extension agent. They’ll probably not take you seriously but do direct them to googling “duckweed for animal feed” or similar and they’ll get up to speed quickly.


  15. February 24, 2014 3:55 pm

    Excellent write-up. I certainly love this website. Stick with it!


  16. Cindy prindle permalink
    February 22, 2014 9:10 pm

    This article drew me in also about 4-5 mos ago but since then not many of the posts have been about duckweed. Rather disappointed at the moment but hoping for more come warmer weather.


    • February 23, 2014 7:06 am

      Cindy, what are you looking for? Yes my ponds have three inches of ice on them. I still work on duckweed projects every day but in an international context.


      • Cindy prindle permalink
        February 23, 2014 4:56 pm

        I’m new to aquaponic & want to grow duckweed for my tilapia as well as my chickens & goats so any & all info I can get on the subject is welcome!!


        • February 25, 2016 10:13 pm

          Cindy, grow your duckweed and feed fresh to tilapia in addition to a reduced amount of fish feed. Some people raise tilapia 100% on duckweed but if you want faster gains, go with at least 30% feed. Chickens- feed fresh duckweed as a supplement for better color in eggs and meat. Dry duckweed can go up to 25% inclusion in feed formulations. They won’t eat it dry and fluffy though. You’ll need to pelletize it along with your other ingredients and then crumble. Also, chickens are not used to it normally, so you will have to teach them to eat it. Withhold other types of feed for a couple days and just give them fresh duckweed.


  17. February 22, 2014 6:09 pm

    Hey There. I found your blog using msn. This is a very
    well written article. I will make sure to bookmark it and return to read more
    of your useful info. Thanks for the post. I’ll definitely comeback.


  18. October 26, 2013 10:47 am

    My family and I are just starting with Aquaponics and I’ve been doing a lot of research. Today the topic is Duckweed, we want to grow duckweed in our fish tanks, but it doesn’t look like that is very practical, since our grow beds cover most of the fish tank, which will limit the light that the fish tank gets, plus it looks like the the water from the grow beds flowing back into the fishtank will disturb the duckweed growth. So, will duckweed grow at all under these conditions? or would we be better off to make shallow tanks specifically for the duckweed and then feed it to the fish?


    • October 26, 2013 11:59 am

      Hi Cindy. Duckweed can grow with only 20% of available sunlight. Of course in the winter, that ratio may need to be bumped up. Your fish will probably out-eat duckweed grown in their tank. Duckweed can handle some water movement though. I’d opt for separate dw tanks with more sun. If you wanted to TRY to throw some duckweed in your fish tanks and watch what happens- cool. Usually I don’t recommend it but if your tanks are well-oxygenated already, it might work. If you want to remove duckweed from a fish tank, I stumbled on a great little DIY project to make that happen easily:
      Watch the video on this page: This guy makes it SO… easy.


  19. September 8, 2013 12:46 am

    i plan to grow duckweed or azolla on slightly bigger scale,say 1 hectare to produce feeds for the free range chicken we have in the farm. at present it is a toss up between duckweed or azolla. which do you think is better, duckweed or azolla?


    • September 8, 2013 7:24 am

      Hi Glen. I don’t know where you are located, but that might play a role in which plant you choose. Azolla cannot tolerate freezing weather. Duckweed produces turions and sinks to lower, warmer levels- even down into the mud at the bottom of a pond. Duckweed grows faster than azolla and is easier to digest. I am not an azolla expert but have grown it a few times and appreciate its ability to fix nitrogen due to the Anabaena bacteria that form a symbiotic relationship with it. I’ve seen it being fed to pigs and chickens in S. America.
      Just to be fair, I’d say do test trials in smaller ponds or kiddie pools, then decide for yourself. During the hot summers, duckweed outcompetes azolla.. I like azolla but I LOVE duckweed for its versatility, growth habits, robustness, protein content, ease of harvest, and looks. That’s just me. 🙂


  20. Francisco & Monika permalink
    August 24, 2013 9:21 pm

    Hello, My wife and i are thinking about growing DuckWeed indoors during the winter to feed our Ancona Ducks some greens during the winter we live in the Fingerlakes area of Upstate NY. I have never done this and thanks you for the info you posted here. Can you suggest what kind will be better for our Ducks and Chickens? and if you can mail me some i will pay for it.

    Thank you


    • August 26, 2013 7:27 am

      Any species will work just fine. The trick is to grow enough in the winter to feed green-deprived farm animals. Do you have a greenhouse where you could set up shallow temporary ponds? If it gets down to freezing, you will need to introduce additional heat, hopefully from a sustainable, free source. Otherwise, roll with nature and wait again until spring.


      • Francisco & Monika permalink
        August 26, 2013 9:08 am

        Yes we do We have a 2 1/2 insulated car garage i will set up 4 small kids pool to grow it there and go outdoors in the spring time.they are going on sale soon ( end of the season )


        • August 27, 2013 7:30 am

          How are you going to keep light on your kiddie pools in a garage? Do you have sky lights or a south-facing large window?


    • August 27, 2013 7:31 am

      Also, if you email me your address and specify how much duckweed you want, I can send it to you.


  21. August 16, 2013 8:56 pm

    Hi there, just wanted to mention, I enjoyed this blog post.
    It was helpful. Keep on posting!


  22. Amanda permalink
    August 4, 2013 10:28 pm

    HI! I am working on a science project for school about duckweed and I stumbled upon your website. It’s awesome and very informative! I started growing my own but I stumbled upon a few problems. I just got mine shipped in from amazon a couple of days ago, but when I started growing them in containers of houseplant fertlizer, they started to turn a very deathly shade of brown. At first, I thought I was killing them because I put them under the sun, so I scooped in some of the surviving ones into another container and put them under the shade. However, they still started turning brown, so I’m starting to worry. When I researched online to see what dead duckweed look like (by the way, I’m using Lemna minor, thought that would be useful information xD) they all said it would turn white. So I have a feeling that they’re not dead, but instead it’s something else. Do you mind helping me a little bit? It would mean so much to me! Thanks!


    • August 5, 2013 7:25 am

      Amanda, love your science project. Even fails are great if you learn from them. In this case, the duckweed is dying. Using garden fertilizer alone in the water is a tricky way to grow duckweed. I’ve had some success but usually not as the pH gets out of whack.
      Here is what I recommend these days for transplanted duckweed: Use water that has sat out for a day to release all chlorine. Add a cup of soil per two gallons of water for micro nutrients. Add a pinch of sea salt if you have it. Release new duckweed into this mix and park in semi shade for a week to adjust to its new surroundings. If it is beginning to grow, you can give it a bit of garden fertilizer but just a tiny pinch. (or a tiny bit of aged manure if you can find it) Go easy on fertilizing it overall. The dirt will help buffer the water pH so when you DO add fertilizer, it won’t cause the pH to shift wildly.
      If the water temperature gets in the low 90’s, you will experience die-off. Therefore in the hot summer months, semi-shade is safer. You can always add cooler water from a garden hose to cool it off.
      Send me your address and I’ll mail you some new duckweed. All I ask is that you pay me for shipping so I can continue to pay it forward.

      Liked by 1 person

      • Amanda permalink
        August 9, 2013 11:15 pm

        Hi Tama,
        Thank you so much for this information! And also, thank you for offering me the duckweed, but I already ordered duckweed before I saw this. If my new ones die out, I may take up your offer again 🙂 Actually, I just got my new duckweed yesterday and I just put them in a solution according to your instructions. I hope it will be better now 🙂 So it was the pH that was the problem; I wanted to test the pH of my water but I unfortunately had not gotten pH strips yet. I ordered them on amazon a day ago. And I agree, duckweed that is shipped in isn’t very fresh and most of them die very quickly. Maybe that’s another reason why they turned brown? Again, thank you for everything!

        Liked by 1 person

  23. February 1, 2013 9:32 pm

    I may be late to the conversation, but I am curious about how the duckweed would be used. Human consumption? Animal feed? Would chickens eat duckweed (obviously ducks do…)?


    • February 1, 2013 9:39 pm

      Oops. Nevermind, I found the website where this is discussed. Intriguing. I’m thinking we have an ideal setup to utilize this to cut chicken feed costs while recycling their manure…


      • February 2, 2013 8:09 am

        Desert Cat, am not sure if you meant my site or another. Try my animal feed posts, or and join our LinkedIn group: International Lemna Association for answers from our duckweed growers and researchers. Your blog pics of your farm are beautiful. Never knew the science behind how to put up a wire fence. (Also, your disclaimer cracks me up.)
        As far as chicken manure, I’d let it decompose or run through a biodigester, then dilute. You could use multiple dilutions to see which one duckweed grows best in. I wouldn’t feed it back to my chickens (cross-pathogen issues perhaps) but instead use it for fish, hogs, cattle, etc… Cheers! Tamra


  24. February 1, 2013 12:11 pm

    It is normal. It is prablboy hair algae. Nothing wrong with it and it is actually healthy as long as it does not take over. You might have more problems with pond scum algae or water algae but since your water is clear dont worry.


  25. Ken Knight permalink
    September 25, 2012 10:31 pm

    Hi- Love your blog. I’m wondering if there is any way to incorporate duckweed into a closed-loop aquaponics system so that it doesn’t take over the entire system? Frequent changes of water seems like a waste of water and the benefits of the duckweed to an aquaponics system. But how would one keep it from invading the whole enchilada? Is there any way to sequester it? I look forward to any thoughts you might have on this.
    Thanks, Ken


    • September 26, 2012 7:17 am

      Ken, I don’t know your set-up, but do know that it is hard to sequester duckweed to only one part of your system as the daughter fronds are small and easily siphoned off, despite your best efforts to screen them out. I do have a few ideas. 1. Go with a larger species of duckweed, such as Lemna gibba. 2. Insure that your outlet pipes are well below the surface of the water so as to not disturb the duckweed layer any more than you have to. 3. Use a series of fine mesh screens for your return water from a duckweed remediation pond. 4. Get a herbivorous fish like tilapia or a grass carp to live in an interim water space as they love duckweed.
      Thanks for reading. Good luck!


      • Ken Knight permalink
        September 26, 2012 9:18 am

        Thanks for the ideas. I’ll let you know how it goes.


        • February 4, 2013 4:53 am

          we had a barrel pond too and the fish awalys died until we got a pump the person at the water garden store said that the oxygenating plants don’t work when the sun is down. the pump did the trick until the evil racoons came


  26. July 12, 2012 4:16 pm

    How thick does duckweed get? How thick can it get and still remain healthy? What happens if it is allowed to go past ‘harvest’ time? Does it rot and stink or anything? Or does it just stop growing?



    • July 12, 2012 6:02 pm

      Hi Susan, the sort of short answer is that you will want to aim for a covering of duckweed all the time to reduce chances of algae taking over. However, how much is too much? The answer is a bit different with each species. Bigger fronded varieties like Spirodella can withstand less layering on itself than say, Wolffia. With Spirodella and Lemna minor, each successive layer gets less and less light and nutrients and a once-thriving stand will self-shade (or self-mulch) within a few days. At first, the lower fronds quit dividing, then the roots lengthen and the undermass starts getting darker and darker to where the lower fronds die and begin not smelling so great. Wolffia on the other hand- I’ve harvested Wolffia that was over an inch deep and all appeared green and healthy. Perhaps as Wolffia has no roots to get entangled, any that die simple drift to the bottom of the pond.
      If I find a batch that is “over-ripe”, I try to harvest just the top, brighter green duckweed and put it aside for a bit. I then harvest the underlayers and use them in my compost or as mulch for something that isn’t up close to the house. It’ll smell for a day or so and you’ve just got to let it air out. The green duckweed is re-released in the pond if I know the water is a healthy environment. This doesn’t happen too often as I use any spare duckweed on a pretty continual basis. However, if you go on vacation in the heat of the summer, it’s a good idea to have whoever feeds your dog to do a bit of duckweed harvesting every couple of days and run a water hose to “rain” on your growing ponds to insure a healthy stand.



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