Azolla & Duckweed Ponds
We can grow all our own fish and chicken food.
The growth rate, chemical composition and amount of biomass harvested from duckweed/Azolla depend on many factors. These include nutrient concentration in water, water temperature and pH, sun exposure and day length, and wind speed.
Duckweeds grow at water temperatures ranging from 6 to 33°C, and at pH of 5 to 9. The optimum growth conditions for high biomass production are water temperatures between 20 and 28°C and pHs between 6.5 and 7.5. To prevent excessive changes in water temperature, duckweed ponds should be at least 30–50 cm deep.
Because duckweed is susceptible to being moved by wind and to water currents in water basins in which it grows, wind speed in the duckweed-growing area should not exceed 0.3 m/s. To avoid wind drifts, water basins are divided into cells or compart- ments (2 to 5 m wide by 4 to 8 m long), which stabilizes the growth conditions (FAO, 1999; Iqbal, 1999).
Duckweed prefers slow moving water however, you will notice fastest growth with areas of agitation. Slight agitation, such as where an outlet flows, seems to increase the asexual reproductive process. The duckweed divide quicker.
Grow in several places. You will find the best micro-climate for production this way. Also, if one spot fails, you have several others producing.
Do not grow in the same area as you are raising your fish. They’ll eat your crop.
Surface Area! The more you have the more you will get. Duckweed needs only a few inches of water, but takes as much space to spread as possible.
Duckweed grows faster in warmer weather. If you want faster yields, make sure your water temperature is over 70°F.
If your duckweed is turning white, something is wrong. The duckweed is dying.
Don’t forget nutrients! Duckweed needs more than water and sunlight to grow. We use the tilapia waste water to grow our duckweed, but you can use other nutrients. Compost teas or organic hydroponic nutrients also do well.
Not all duckweeds are equal. We have experimented with several different species of lemna and have found that lemna minor is our favorite duckweed for production.
Duckweed has the smallest flower in the world, but we have never seen it. Don’t worry about pollination as means of reproduction. The plant grows and divides asexually, much like a single-celled organism does. Don’t worry about finding tiny bees.
Duckweed can grow thick! When production is highest, duckweed can grow several inches thick. We have had our pond area full before and it looked like a lawn.
Don’t forget to add oxygen. If you place duckweed in a pool without aeration the water will eventually go anaerobic. Without oxygen, nothing will grow.
If you grow in an aquarium you may grow more algae than duckweed. Duckweed naturally limits the growth of algae because duckweed floats and gets the light before the algae. In aquariums this does not happen.
Yes, duckweed can be grown and fed to dairy animals, small ruminants, poultry and ducks. One small pond of 4’X8’X1″ duckweed would yield about 1/2 kg of green fodder protein on a daily basis at literally ZERO cost. Cows and buffaloes relish eating them, once they get used to them. (https://www.researchgate.net/post/Can_fresh_duckweed_be_used_as_fodder_for_lactating_dairy_cows)
How to build large duckweed ponds
Here is a video showing large duckweed ponds.
You can also build smaller ponds as “roofs” on many other structures, such as a floating pond as a cover on the fish tanks, or a duckweed roof as part of the chicken pen. This makes the feeding easy as the duckweed is available where you feed your animals.
We should grow Azolla and Duckweed. Azolle grows better in our winter – and Duckweed grows better in our Summer.
Grow it in various places with different shade/sun etc – so if you kill one pond full you still have the others.
The pond should be shallow so it is warmer. Keep Guppies to keep the Mosquito Larvae in check. Do not add Tilapia to the Duckweed Pond as they will eat up all the Duckweed.
Your pond should be about 15cm deep – about one brick height.
You need some air in the water – so you need some tool like a pump to make bubbles in the water.
Duckweed is high in Protein and thus an ideal Fish Food.
Put Cow Manure into the Pond every two weeks to keep it fertilized
I’ve been saying all along how easy it is to grow mega crops of duckweed, IF you know the tricks!
Duckweed grows on benign neglect in the wild. However, to cultivate it in a garden setting, duckweed does have a few definite needs if it is to thrive consistently.
1. Like any vascular plant, duckweed needs a minimum of nitrogen, phosphorus, potash and micro nutrients. Sources can be as simple as a little humus and/or soil or compost tea. To achieve high protein levels of 40% or greater, duckweed needs added nitrogen, preferably in the form of ammonia from animal waste. This is why it thrives so well in fish aquariums.
Nitrogen sources can include fish wastewater, chicken coop drainage, some types of grey water, vermiculture liquor, or aged manure. If a solid, place in a gunny sack and lower into the water column. This releases a steady amount of nitrogen and trace elements for a couple of weeks. Replace if you see duckweed roots grow to an inch or longer. Some people will occasionally spray the duckweed with an organic-based foliar spray as another source of nutrients.
2. Duckweed thrives at a pH of 6.0 to 7.5 If algae is present in large quantities, it can raise the pH to dangerous levels by virtue of CO2 production at night. The trick is to monitor pH, especially if algae is present. Treat pH extremes as described in my prior post. Encourage an adequate surface covering of duckweed at all times to suppress algae production.
3. Harvest duckweed as needed but leave about 1 1/2 to 2 pounds of wet duckweed per square meter on the surface of a pond daily. This insures enough of a cover to slow down algae growth or suppress it altogether. As an added benefit, this much covering also helps with mosquito control, water evaporation and temperature issues. More than 2 1/2 pounds of wet duckweed per square meter will result in its demise, as it self mulches at that concentration.
4. Duckweed prefers water temperatures of 10 to 32 degrees C. Above or below that range, duckweed just sort of sits there. Much above 90 degrees, your duckweed crop will crash and it won’t be pretty. Ways to circumvent this is light shading from surrounding trees, plants or shade cloth hung over the growing area.
5. Keep water movement to a minimum. As duckweed floats on the surface, any strong wind will push it to the edge of the pond where it will begin to pile up in layers, effectively self-mulching the layers beneath. Grow taller food crops around the perimeter to shield it from the wind.
Duckweed is an amazing crop that gives much more than it gets, but still needs a few basic “gotta haves” in order to reach its full potential in a garden setting.
Here’s a detailed video on building a duckweed pond and producing duckweed:
Here is a very detailed video – about 40min long – a proper class on duckweed. https://www.youtube.com/watch?v=VBJUx9M5MGs
Duckweed grows best if you give it nutrients. This is as easy as putting manure or dung into your water. You can also use worm tea or fish waste. Put some into your pond every three to four weeks or when you see the plants go yellow.
Also replace your water every three months. You can use the water to water your other garden plants, they will love it.
Plants need to breathe, so you need to put oxygen into your water.
We can build a very simple tool that helps to add oxygen into the water. We build a vertical wind turbine.
Here is some background info:
Detailed video on fertilizing the Duckweed/Azolla pond
Take out ¼ of the duckweed each day. It will grow back in a day. So if your pond is 1m x 2m, then you can take out 1m x .5m of duckweed every day.
You could also take out half the duckweed every second day. Just keep the whole water area covered so that algae do not get light and start growing.
If your duckweed turns yellowish it is busy dying and something is wrong – the Azolla will get smaller and eventually disappear.
Mosquito can grow in your ponds. Simply put in some Guppies..
For scientific work on Duckweed as an animal feed:
A detailed book by the FAO:
Use of dUckweed (Lemna L.) in sUstainabLe Livestock prodUction and aqUacULtUre – a review* *
Marcin Sońta, Anna Rekiel, Martyna Batorska♦
What about Azolla?