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Duckweed as Fertilizer for Citrus Grower

March 2, 2012
Moat of duckweed surrounds Fruit Orchard

Moat of Duckweed Surrounds New Orleans Citrus Orchard

Imagine using a duckweed-based fertilizer/mulch to produce prize-winning oranges and Satsumas.

Where most people would see a green blight on their pond, Isabelle Cossart of New Orleans sees a healthy, money-saving alternative to fossil fertilizers and trucked-in mulches. Isabelle rakes duckweed from a moat (yes I said a moat) around her property and applies it to her citrus orchard as a green mulch and fertilizer.

I connected with her last year after reading a NY Times article about her lifestyle post-Katrina: A lifestyle that includes running a very successful citrus orchard. What caught my eye in the article photo was the presence of duckweed, lots and lots of it. I connected with Isabelle to find out if she was taking advantage of it.

Isabelle told me that she routinely harvests the duckweed and uses it to mulch her trees in order to keep weeds down and add fertility to her soil.  Duckweed saves Isabelle on overhead expenses as a replacement for both mulch and fertilizer combined. She said it works great and was very pleased with the results.

Most gardening experts advise to compost all green biomass prior to adding to garden soil, so Isabelle’s use of fresh duckweed intrigued me. I decided to try it for myself on a plot of tomatoes and noticed an increase in growth, with no burning or yellowing due to lack of nitrogen or iron. The jury is still out on raw duckweed as a mulch as I plan to do more testing this summer.

Isabelle also mentioned that when the water surface is fully covered with duckweed, she isn’t bothered by mosquitos. There are two schools of thought on this. Research suggests that the covering of duckweed on the water surface inhibits mosquito larvae growth by preventing them from breathing air. The second is that duckweed perhaps releases a chemical that represses or kills mosquito larvae. Some research has been done on this, but nothing conclusive yet.

Isabelle also noted that the frog population has multiplied rapidly in recent years. She said,”The frogs love the duckweed as security and a food source.” A covering of duckweed also serves to reduce evaporation by 50% and keep the water cooler.

Duckweed- gotta love it.


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