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Winter Growth of Duckweed

November 28, 2012

My outdoor duckweed ponds had a light glaze of ice over them this morning. Even though I was prepared to watch my floating duckweed succumb to winter’s grip, I had the urge to run out there, melt the ice and truck all that duckweed into the house. Don’t know what I’d do with it as I have plenty indoors, but the urge to save it all was a strong one.

Imprisoned in the ice, the duckweed will stay green for quite a while and fool you into thinking it’s still healthy. In years past, I’d  break loose a chunk of ice and revive the duckweed indoors, only to watch it die. What survives are the starchy turions that formed during the fall and sink to the mud below. Come spring, they to begin growing again and rising up to form full-fledged fronds.

My indoor containers are sitting in a five foot broad expanse of windows in my “sunroom” and  growing madly. (It’s actually my tool room, wood working/storage area with a saw dust path kicked through it.) I actually have to harvest every few days or the duckweed gets too crowded. My excess is being used as green mulch around my avocado seedlings who are equally happy in the cool room.

I had these duckweed batches under fluorescent lights for about three weeks. They were growing well but I was forced to move them to my sunroom because I had to go on a trip for five days and couldn’t turn the lights on and off. I only hoped they’d get enough light out there. To my surprise, the duckweed is doing better in an unheated room with weak sunlight than in a 72 degree room with lots of artificial light.

Living and learning…

4 Comments leave one →
  1. Susan Munroe permalink
    November 29, 2012 9:02 pm

    I wonder if the turions need the mud? I have two small (12″ dia.) containers in a cool bathroom, sitting near a north-facing window. The water they’re in was dipped off the top few inches of the ducks’ wading pool (poop settled on the bottom) for liquid nutrients. But there is no mud.

    Looking at the duckweed, the leaves are not multiplying, but the roots do seem to be enlarging and tangling/growing together. I wonder if the turions need deeper water, or if 4″ is deep enough for a non-freezing (I hope) bathroom?



    • November 29, 2012 9:52 pm

      Good question… This is the first year I’m holding my duckweed water over in my wading pools until next spring. Two have 1/2 inch of mud at the bottom while the third has scant mud at best. I think it’s probably more about sinking down to where it is not going to freeze rather than sinking into mud. The tangled roots are just that- matted duckweed. Turions are small, darker green buds that resemble the fronds but are mostly starch and therefore 1.5 (approx) times heavier than water. That is why they sink to the bottom..


  2. November 29, 2012 8:02 am

    I visit four established ponds within 70 miles of my home several times a year.. All contain Lemna minor and Wolffia mix. Lemna minor is dominant. During July and August, the Wolffia takes over. Then in September, the Lemna minor makes a comeback. I’ve seen this happen three years in a row. In my personal small ponds, Wolffia makes sporadic attempts to dominance but does not succeed overall. Maybe because the water chemistry and temperature is not that of the natural ponds?


  3. hamdi shaar permalink
    November 29, 2012 12:48 am


    Dear tamra

    In your years of duckweed observation, can you indicate which are the dominant duckweed strains in each season of the year in your part of the world.


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