The Benefits of Growing Duckweed
Duckweed Growth and Benefits
For some duckweed is a menace, for others it's a Godsend. This plant has the ability to reproduce rapidly, it can double in just 16 hours - 2 days, depending on its growing environment.
This makes it either a formidable enemy or a fantastic ally.
Today I would like to highlight the positive side of duckweed and tell you why we have built specially designed ponds to grow this here on our farm in Brazil.
For those of you who don't know what duckweed is, it is a small floating plant that grows on still ponds. It can cover an area rapidly and because of this can cause problems. Now however, duckweed is being touted as a miracle plant for many reasons including the following:
- Cost effective renewable energy, biofuel
- Water filter
- Mosquito prevention
- Prevents algae growth
- Reduces evaporation on bodies of water
- Virtually free animal feed
- Food for humans
Duckweed as a Water Filter
Duckweed loves muck. It can clean the water from farms which are rearing cows, hogs, chickens etc. The run-off created from intensive farming methods can cause an ecological nightmare if left untreated and allowed to leach down into the water table. Duckweed can clean this water by absorbing the resulting chemicals.
In Palestine, they are looking at using duckweed to clean their water systems as they have very limited fresh water available. Using this natural low-cost water treatment is not only good for the country but the environment as well, it's a win-win situation.
There are various types of duckweed. Depending on where you live, you may have more success with one type over the other. When we began we started with two types. The man who sourced them for us said one preferred shade. For us, that was a non-starter as ours was in full sun most of the day. We started with a tablespoon of each type.
If you keep it alive in water, until your ponds are ready, you will be fine.
Control of Mosquitoes Using Duckweed
Mosquitoes love shallow still pools of water to lay their eggs in. This is a major problem in many countries, not just third world countries. Duckweed could be the solution in many of these areas.
Because duckweed covers the surface like a thick blanket, it blocks the mosquito from laying eggs. Malaria, yellow fever, dengue fever, and the Zika virus are the four main diseases spread by mosquitoes here in Brazil and other parts of the world.
Stop mosquitoes breeding and you drastically reduce the number of illnesses and deaths attributed to them. According to the World Health Organization (WHO) mosquitoes are endemic in 91 countries and affect 40% of the world's population. Diseases transmitted by mosquitoes are estimated to kill 2.7 million people per year.
Duckweed as a Bio-Fuel
Scientists are working on ways to utilize duckweed as a bio-fuel. With the rapid reproduction of this plant, it has not only the scientists but also the environmentalists taking notice.
Other plants are being grown for bio-fuel but none grow with the rapidity of duckweed. Currently, the main bio-fuel crops are
- Corn (maize)
- Elephant grass
- Sugar cane
These take up vast areas of farmland, often in third world countries, which could be used to grow food crops for the local population instead of crops which will be made into bio-fuel and sold to the westernized first world countries.
The advantage of duckweed is not just its speed of growth but because it grows on water, it frees up the land for farming food crops. Plus with its water purifying properties, it leaves clean water behind.
Duckweed as Tilapia Food
The reason we decided to grow duckweed was to feed our tilapia. My husband and I have a small farm in northern Brazil where we raise tilapia for the local market.
We are growing the duckweed to use as a supplemental feed for the fish. The high protein content of it makes this an ideal food for them. Although we feed them this astounding plant, this alone will not sustain the fish as a complete food source. We still feed them a commercially prepared pellet food every other day as this ensures all the nutritional requirements of the fish are met. Feeding the fish duckweed has reduced our feeding bill by half!
That is a massive savings when you're feeding several thousand fish.
It isn't just fish that eat duckweed though. We have also fed this to our chickens. If started when they are young, they readily accept it.
In some parts of the Far East, it is being sold and consumed by humans as well. We are also now farming shrimp and these are fed duckweed which has been dried and frozen.
The ability to use a naturally occurring plant has opened up an opportunity for small farmers to successfully raise their own fish for sale or consumption. Where before, the cost of feeding them to adult size, would have been cost prohibitive.
How to Build Ponds for Duckweed
For our five ponds, we hired a backhoe and driver. Depending on how many you are wanting to construct, you may be able to do this manually. You will want the water to be no deeper than a foot. We made our ponds 30 m long by 2 m wide (98' x 6.5') and used a plastic liner in them.
Choosing a Pond Liner
All pond liners are not created equally. For ours, we needed one which was suitable to be used whilst underwater, in the sun and one which wouldn't leach anything toxic into the water which could damage the plants and subsequently cause problems with the fish.
In our region of Brazil, the UV light from the sun is in the extreme category. This coupled with the salt in the air which destroys fabric, plastics, metals meant we needed a high-quality liner. Environmental elements need to be considered when selecting a liner.
Remember, when you calculate the dimensions, you need to leave enough for the ends and the sides.
Once you have laid this in your shallow pond, secure it whilst you fill it with water. We went low tech and used bricks to hold it down from the constant wind we have here.
Getting Your Duckweed to Grow
Your duckweed pond will require feeding. This is done with manure which has been soaked in water. We use a large 100 liter plastic trash can for this purpose.
My husband puts the manure in, (we use chicken) and then fills the trash can with water to allow it to soften. Then he buckets this mixture into the ponds. Onlookers should stand well back as there will be splashes. You will know in a couple of days if you have the mixture correct because you will have a rapid growth of duckweed.
If the roots are long, more than a couple of inches, you need more manure. The roots are trying to stretch out and find nourishment. This is why the ponds are kept shallow.
Harvesting the duckweed is easy. We simply use a swimming pool net on an extendable aluminum pole. This is a quick and efficient way to scoop it out. The weight of the water laden duckweed can be heavy. I found it beneficial to walk to where I want to scoop from, scoop it out and allow the water to drain off back into the pond. The further away you are using your net, the heavier the duckweed will feel. Move closer to where you are working from and save your back.
This is also a good way to remove any leaves which may have blown in. If you live where there are trees, it is a good idea to put up a barrier such as chicken wire or plastic fencing to keep as many leaves out as possible.
Always clean your net after using to prevent any bits of duckweed from dying on the net and causing a blockage.
Overflow for Ponds
My husband made an overflow system out of plastic pipe and Coke bottles. We can get downpours that last several hours and deposit an enormous amount of water in a short time.
Because duckweed floats, we needed something to allow the water to flow out but not carry the duckweed with it. This is a simple but effect method.
Also be aware, after a heavy rainstorm you may need to add more manure, as the fresh water will have diluted your ponds.
Wildlife in the Ponds
Many a night, during the mating season, we have many frogs in the duckweed ponds. We encourage everything here with the exception of cane toads.
There are beetles and other aquatic life which have made their way into the ponds on the feet of herons. It is always a good idea to inspect the pond for things living in there, quality of the water and the condition of the liner. This can be done as a matter of course when you are harvesting your duckweed.
Cleaning the Pond
If you are using manure from a chicken farm, you may end up with sawdust debris in the bottom of your pond. It is a good idea to drain it occasionally to clean it.
Draining can be done through evaporation, siphoning, or by using a bilge pump. If you have never siphoned off anything, it's simple. Put one end of a hose in your pond and the other end at a lower level. Suck on the end until water begins to flow out. Remember, you've added a lot of manure to the water, and you don't want to drink that.
**If you only have one pond of duckweed, keep some of your plants in a jar of water to use as a starter.
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This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
Questions & Answers
What time of year can I introduce duckweed, so it doesn’t die off in the cold? I live in St Andrews, Scotland.
For introducing it, wait until any chance of frost has passed. However, once it is established, it can overwinter and stay green according to the RHS. We have noticed it will still return, the following year even if the area is dry. It goes into the mud and waits to resurface and start reproducing when the rain starts.Helpful 7
I have a pond covered in duckweed and want to sell it. Can you suggest how I can do this?
You have various options, and some may be better for you than others depending on where you live.
You can sell online on sites such as eBay. There are restrictions such as sending abroad, that is forbidden in many countries.
Sell it as chicken feed to local farmers. For this, it may be better to dry it first.
Sell it to fish farmers or those who are doing aquaponics with fish.
If you have a local pet store that has aquariums, see if they want to buy it to resell.Helpful 7
Why do you want to harvest duckweed?
We harvested our duckweed to use as food for our tilapia. We used it as a supplemental feed every other day. This reduced our feeding bill dramatically.Helpful 15
How long does the common duckweed live?
It's a good question but I can't answer that. I'll explain why. When we were first given ours for our ponds, we were given about a tablespoon of two different types. The man had kept them in a bottle for about a week before arriving at our farm.
When we put them in our ponds, they began reproducing, so I have never kept any back to see how long one plant would survive, they just keep reproducing when in a suitable growing medium.
I do know that even when an area that had duckweed dries out, when it becomes wet again, the duckweed is likely to return.
If you are thinking of ordering online and hoping they arrive in good condition, the supplier generally gives you extra to cover any potential loss. Remember they grow fast.Helpful 11
Do you have a problem with the water in your shallow ponds getting too warm under the sun, especially with black liners? Won't that kill the duckweed? Also, do rainstorms/wind kill the duckweed?
The answer to both of your questions is no. Remember, in the wild duckweed will be growing in a pond which likely will have a build-up of silt and so will be dark and shallow. With regards to the rainstorm, the problem could be that it would float out of your pond as the water rises. In the photo, you'll see a low cost (virtually free) method of creating an overflow system so the water flows out and the duckweed stays in the pond.
Where we live, it is 87°F (30°C) year-round and we get a UV index of 11 which is in the extreme range. We also have a constant wind for several months. What I would suggest is find a duckweed that grows local to you, and then you'll know that it will survive in your conditions.Helpful 6
© 2012 Mary Wickison