Getting Rid Of Pond Duckweed Without Chemicals

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Duckweed in a pond is an interesting situation. Some pond owners (particularly those with smaller ponds) often love having it around, and sometimes add it to their pond and would never dream eradicating it.

By the way…I talked about duckweed in this pond tip just in case you might wonder what it looks like and how it differs from algae.

Large pond owners however usually have a different opinion of duckweed. For them, a little might be ok, but often, when conditions are right, duckweed can grow like crazy and cover the entire surface of a pond.

The plant actually isn’t all bad to have around. It’s a powerful user of any organic nutrients in the water so in a sense, it can help clean and balance the pond out. And it will go away when and if the weather cools enough in moderate climates.

Even with all this, many pond owners want to treat it, and in terms of chemicals, they’ll often resort to something with Fluridone in it. Some brand names of products with Fluridone include Sonar or WhiteCap. These treatments are quite expensive with small amounts, such as 8oz. costing several hundred dollars.

Fluridone is best used really early in the growth cycle when the plant is weaker and it will provide better control that way.

By the same token, we have had success in lowering nutrient loads in a pond with a beneficial bacteria treatment routine before the duckweed starts growing well, and in keeping nutrients low, it will have a more difficult time taking off. Wait too long though, and a bio won’t have much affect.

The problem with both of these treatments is that most pond owners end up waiting, or getting caught off guard when the plant expands quickly over their pond. And by then it may be too late.

Particularly when temperatures get really hot, as they have been this summer around most of the U.S., it’s not a good idea to treat duckweed chemically. As we’ve stressed time and time again, massive die off of a plant in a pond (usually due to a chemical treatment) will pull a lot of oxygen from the pond, and in doing so, will likely hurt any fish in the pond.

So what’s a pond owner to do about duckweed?

Well there is one option (actually several, but no other works as cheaply and effectively over a wide area), and it totally eliminates the need for any additive in the pond at all. It requires some manual labor, but that’s not a bad trade-off in a lot of cases. You can build this DIY removal tool for under $25 and with a little tweaking, you can usually get it to work pretty well.

Watch the video below to learn more…and please feel free to leave your comments and suggestions below.

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15 thoughts on “Getting Rid Of Pond Duckweed Without Chemicals”

  1. Just a note here. There’s no real limit to how many ties you can put on the rope. In some sense it could be said that the closer the better and the more the better. This video is really just a suggestion of a good direction to go, and then experimentation will show what will work the best for you.

    Best wishes!

  2. What a great idea Mark!
    my pond is not very big, and so far, I don’t have any duck weed yet,
    but I always like solutions to problems that I can do my self with out chemicles.
    Malibu, CA

  3. Instead of a noodle buoy have you tried the foam pipe covers used to winterize outdoor pipes? They are smaller and already cut and can be secure to the rope with the wire ties.

  4. I think the pipe covers would work well too. I’ve also heard about some floating poly line…that may work even better and may not need floats of any kind. Worth trying I think.


  5. This worked very well at removing a thick mat of duckweed that covered my pond. I cut the “noodles” into 1 inch sections, spaced about 1 foot apart, which allowed the rope to float on the pond surface. I removed about 95% of the floating weed using this technique in three session over the span of about ten days. I am composting the biomass. As you practice, you’ll get more effective.


  6. Well I made my skimmer and I must say it does work. I would however say that it seems to need more weight. I used a nylon rope with the pipe covers. The nylon rope itself floats and followed the directions to the letter in the video. However when using the skimmer it doesn’t work well when going over or through lily pads or other aquatic grass. Another key to success is you must go slow in bringing the skimmer across the pond. If you hurry you can go right over the duckweed and lose everything you have gathered. You can hook one end of the skimmer to a row boat and have the other end on shore and simply make a big circle and then rake duckweed onto shore. We have a rather large pond and I would say that we have over 3/4 of the duckweed removed now. If anyone has ideas as to how to weight this down so it doesn’t float over the duckweed please post.


  7. Scott,

    Here’s a thought. And I’m going to try it myself. I plan on using water skiing tow line which is a hollow braid polypropylene line. I’m going to open up the braid and insert rocks as needed in the braid. Since it is hollow braid, the harder you pull the stronger it will lock whatever is inside the braid.


  8. This works pretty well – pretty much cleared the duckweed and the long weeds underneath without floats. Thanks. 22 years with my two-acre pond and never had a duckweed problem until this year. Maybe it is because some of the grass carp died – and I missed the opportunity to replace them cheaply through the farm store this spring. So I bought a 100′ 3/8 rope – twisted not braided because I wanted the 244lb not 200lb working strength. I bought 120lb 8″ cable ties (very stiff) instead of 50lb strength ($24 for 200 plus $10 for rope). I put the three ties about a foot apart because, well, they are expensive, and I’m lazy – assembled it while watching a movie. I also left about 30′ of rope for throwing across parts of the pond since I don’t have help, and I got tired of putting those ties on. Next step is to put some weight on to really get the weeds underneath – might use the tractor to gently pull it all out. Thanks again.

  9. Hi Brad,

    To be honest I’m not sure how well this would work on string algae. Duckweed is or could be quite a bit lighter in density and weight than some string algae growths. If the algae was light enough it might help some but if it’s heavy, probably not.

    The ties actually catch on the small roots that come off the duckweed pods and that’s how they kind of get grouped together so the line can skim them in mass along the surface of the pond.

    Reports have been pretty positive overall on how well this worked for some folks. It’s probably not the final solution to the problem but it’s cheap and helps a few folks get a clearer pond.

  10. Worked like a champ! Probably got 70% of it on my first pass, and I had a THICK carpet of it on my pond. I’ll probably do another pass or two to get the rest. Thanks so much for this elegant, clean, and inexpensive solution!

  11. It should help remove watermeal too…it would work best on duckweed since it’s better but you should be able to make headway on watermeal too.

  12. I’m planning to put a koi pond in the yard next year, and I’m glad I came across your article. There are so many things to think about when putting in a new pond, and I’m grateful for this helpful tip that will hopefully keep me from having a frustrating duckweed problem in my pond later on down the road.

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