Carpets of duckweed

I know as much about water gardens as I do about growing orchids, but from reading posts on favorite blogs like It’s Not Work, It’s Gardening! and Danger Garden I have at least heard the word “duckweed.” It seems that for folks who have a pond or water garden, duckweed (Lemna and other genera) is something desirable although in some circles it’s considered invasive.

Yesterday I joined my friend Ursula for a walk through the UC Davis Arboretum, and we saw some pretty impressive carpets of duckweed in Putah Creek. According to signs posted along Putah Creek, gray water from campus is released into Putah Creek during periods of drought to raise the water level. Whatever is in that gray water sure is good fertilizer for duckweed!


And there are plenty of ducks seemingly sitting on top of carpets of duckweed.





Do ducks eat duckweed? This article says “Yes and no. Domestic ducks tend to eat duckweed, wild ones don’t.” I consider the ducks on Putah Creek to be domestic, so maybe they do.

The same article continues:

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.

Very interesting. I wonder if UC Davis is studying duckweed as a biodiesel feedstock?


It’s odd to be writing about water gardens and water plants when we’re at the height of a four-year drought and a 6,700 acre wildfire is raging not far from here…


  1. Yikes! Hope that fire subsides...

    I think it's attractive but it seems to be the bane of many a big water feature owners. Not a problem for koi ponds though as they everything...

  2. I have a love/hate relationship with duckweed. In the past I loved it, when the tank pond was in more shade. Last year I hated it, as it took on an ugly bleached yellow color in the sun. This year, I didn't introduce any, and I've no regrets. I do love how bright green it is in your photos.

  3. Wow, that's a lot of duckweed. It's kind of pretty and green. I grow it in a couple of water filled containers and enjoy it. When there's too much it goes in the koi pond to supplement their diets.

  4. Duckweed, Azolla and and Giant Water Fern (Salvinia molesta) can really be a bane. I try to remove them from my water gardens whenever possible. Just a few tiny plants can multiply and cover and entire water garden in a very short time.

  5. I've always thought of duckweed as a bad thing but I'm glad to hear that a) the ducks can eat it (if so inclined) and b) that it could be used in biodiesel. I hope that fire gets under control soon - I'm sure your air quality is poor and I know how unnerving it is when those fires get close. (My in-laws lost their home in Malibu to fire more than 20 years ago but the memory is still vivid.)

  6. The bane of our pond is string algae, which comes close to clogging the drain once a year or so. grrrr! Don't think duckweed would be an improvement, tho.

  7. My goldfish gobble up any duckweed that grows or that I put in the pond. I don't know if they could eat THAT much though! :)


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