Duckweed has many uses but brings many problems


That green stuff all over our still waters is probably not algae like most people think. It’s a floating flowering plant without stems called duckweed (Lemna sp.). Its growth rate can be phenomenal. Under good conditions duckweed can double its biomass in less than 24 hours. This means it can cover an acre of water in less than a month and a half.

As one might suspect this aquatic invader is eaten by many species of ducks. The problem

is that the birds don’t really control it. They spread it to other waters. These floating plants cover the surface and eliminate light to submerged aquatic plants, causing their demise.

Anything that dies, whether it is plant or animal, must decompose. This generally requires oxygen, which in aquatic environments is less available than in terrestrial ones. The result is a decrease in dissolved oxygen of the water and that causes problems for many aquatic animals including fish.

But duckweed has many redeeming qualities. It helps purify water by extracting nutrients from it. It has the potential to remove fertilizer nutrients from hog and other animal waste. When skimmed off lagoons and processed it has great feed value for fish and livestock. It’s high in protein and highly digestible.

It’s probably not a great human food source as high oxalate content could pose a problem for kidney stone formers. Small quantities are fine in survival situations as it’s not poisonous and is easily digestible. Bacterial contamination might concern me though. I don’t eat it.

Use of dried duckweed as a fertilizer has potential. It decomposes quickly and provides organic matter, nitrogen and other nutrients to the soil. Skimming it off the surface is a simple process, but removing all of it this way is impossible. Don’t expect to cure your duckweed problem simply by mechanical removal.

Duckweed research is ongoing. Its potential as a biofuel is well documented. Phenomenal growth rate make it better suited for the production of carbon-based fuels than any of our agricultural crops. Several sources claim gasoline produced from duckweed would be competitive with a $72-$100 per barrel crude oil price.

It tolerates a wide range of water conditions too. Duckweed can thrive at a pH range of 4.5 to 7.5. Fertilization is unnecessary. In fact, duckweed removes runoff fertilizer from our waterways, which cleans the water.

All this talk about livestock feed, fertilizer and biofuels mean nothing to you if you have a farm pond and don’t want it overrun with duckweed. There is hope. Several approved herbicides including Diquat will kill it. Proper pesticide certification is necessary, so if you don’t have it please hire a professional. He can also deal with algae, which could result from killing the duckweed.

One problem still remains. If duckweed wants to grow prolifically it means that the water has a high nutrient content. Duckweed may grow, but it doesn’t thrive in clean water. Fertilizer nutrients are coming from somewhere and eliminating the source is the only way to truly eliminate the problem.

 

Duckweed also often grows on my greenhouse floor.

Duckweed also often grows on my greenhouse floor.

Ted Manzer teaches agriculture at Northeastern High School.

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About tedmanzer

I grew up in Old Town Maine and got a B.S. at the University of Maine in Plant Sciences/ minor in Botany. From there I moved to West Virginia and earned a M.S. in Agronomy at WVU. I also met my wife there. She grew up in rural WV as the daughter of tenant farmers who raised cattle and hogs. Their lifestyle at times was one of subsistence and I learned a lot from them. I've always been a foraging buff, but combining my formal botanical knowledge with their practical 'Foxfire-type' background opened up my eyes a little more. I now teach agriculture to high school students at Northeastern High School in Elizabeth City, NC. My wife teaches with me and we make a great team. I also write a weekly nature/foraging column for the local paper (dailyadvance.com) and frequently publish articles in several other newspapers in northeastern North Carolina. I also have written several Christian nature/adventure novels that I plan to publish eventually. One is a five book family saga I call the 'Forgotten Virtues' series. In the first book, Never Alone, a young boy comes of age after his father dies in a plane crash, and he has to make it alone. Never Alone is now available in paperback, Kindle and Nook. The second book, Strange Courage, takes Carl from his High School graduation to his recovery from a nasty divorce. The third book, Second Chances, takes Carl from his ex-wife's death and the custody of his son to his heroic death at age 59. The fourth book, Promises Kept, depicts how his grandchildren react and adjust to his death. In the final book, Grandfather's Way, his youngest and most timid granddaughter emerges from the shadow of her overachieving family and accomplishes more in four months than most do in a lifetime. I use many foraging references with a lot of the plants I profile in these articles in those books.
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