Backyard Aquaponics
A place to discuss aquaponics

“Under experimental conditions (duckweed) production rate can approach an extrapolated 183 metric tonnes/ha/year of dry matter” (Leng, Stambolie & Bell)

This translates into18.3kg per square metre of dry duckweed per year.

Since duckweed is about 94% water, this equates to about 300kg of wet duckweed per square metre per year……a bit less than 1kg per square metre per day.

Bear in mind that this is probably what they achieved in a laboratory under ideal conditions. I'm suggesting that, with careful management, we ought to be able to produce at least 1kg in 3 square metres per day.

Since no-one (as far as I'm aware) except Joel is at the stage where they could use anything like a kg per day, I suggest you start off with a water area that is no larger than you can control as closely as possible.

Here's a few rules:

- Temperature…..about 25oC……not more than 30oC or duckweed becomes stressed - below 20oC growth is reduced. For small duckweed containers, a fish tank heater would be ideal.

- pH…….grows best over the range of 6.5-7.0

- Plant Density……a complete cover of duckweed (and correct pH levels) suppresses the growth of algae which has the effect of elevating pH levels. Researchers suggest that the upper density is 1.2kg wet weight per square metre (above which crowding limits plant growth) and the lower density is 0.6kg wet weight per square metre (below which growth is insufficient to prevent algal blooms).

- Light……I've used flourescent gro-lites to produce duckweed before. Set up on a cheap timer (about $15 at B) and try about 12 - 14 hours per day.

- Nutrition.....this is the most difficult parameter to prescribe but since we're doing aquaponics, the ideal water in which to grow duckweed has to be the nutrient-rich water from a fish tank. It's a balancing act, the more fish (or the larger the fish), the higher the nutrient levels and the more duckweed that can (up to a point) be produced. If light levels and plant density are correct, even traces of nutrient will encourage growth.

Crude sea salt will provide all trace mineral elements…..only tiny amounts required.

Your duckweed plants will only produce for a certain time before they start to decline. Root length appears to be a convenient relative measure of frond-age……it is recommended that you re-seed the pond every 4 – 6 weeks with fresh duckweed

In young plants, root length is also an indicator of protein content…..the longer the roots the lower the protein levels.

If you're going to grow your duckweed outside, protect from any wind and flowing water.

I suggest that you use these parameters to get going and then fine tune nutrient levels.

For those of you who have been eating a bit of duckweed lately:

“There are reports that Wolfia arrhiza, which is about 1mm across has been used for many generations as a vegetable by Burmese, Laotians and Northern Thailand people.”

Gary

Thanks Gary, much appreciated

What is a long root as opposed to short. 10 mm? 5 mm?

I put some on windowsill and roots lenthened overnight in tap water.

Off for two days so I added 25% water from fish and will see if new plants have shorter roots (I theorise they will indeed)

Would reseeding be a breach of the otherwise strict quarantine I employ?

Any history of pathogens or nematodes etc hosted by duckweed harvested in the wild? Method to clean a wild species?

I'm guessing as it reproduces so fast it also deteriorates rapidly genetically. So the reseeding would add genetic diversity?

If a person were to take duckweed from several wild sources and interbreed/seed them from each other... Think this would work?

If these are all answered in those big documents just tell me to read them.

The research literature tells us that root length in duckweed varies and can be as much as 140mm.....depending on the species.

When I got my first lot of duckweed, the roots were very short (about 1 -2mm) but over a period of time I noticed that they became progressively longer to the point where they are now up to 40mm long.

Initially, I thought that another species of duckweed had taken over but then I read that that duckweed with long roots was a result of low protein levels arising out of low nutrient levels in the water.

I now believe that the long roots are the consequence of my reproducing the same batch of duckweed over too long a period.

While I acknowledge the value of quarantine for disease control, every food production system that includes animals or fish (or duckweed it seems) will require the introduction of 'new blood' periodically.

Not all duckweed species are useful in an aquaponic context including (for example) some of the Spirodela species. The two that I read as being most useful belong to the Lemna and Wolffia species.

If you can find a wild duckweed that has the attributes that you want, simply introduce a new batch every now and then. Wild duckweed (particularly from a large body of water) will have the genetic diversity that is needed to keep going indefinitely.

The research literature that I've read doesn't have a lot to say about pathogens or nematodes.

Are these many people out there growing duckweed for their fish?

I think you will find that many people do. Jade perch love the stuff and silver perch will eat it as well
I have several tubs growing it

Me too... and lots of others...

Wow, a thread not posted on since 2006 being resurrected... Hi Gary...

I was growing it until the dog lapped it up off the top of my Sump

i Hate it when that happens . . .

I have 2-30 gallon tubs that I use for growing duckweed. During the summer here in SD the duckweed will double everyday, luckily the Tilapia seem to be able to eat it just as fast as I put it into the fishtank.


Joe

I have set up an old cut down pool fiter as a duckwwed pond outside my chook pen and will be adding a few more to it as I pick them up. Duckweed will be going over the fence to the chooks.

Hmmm i have duck weed in a bucket with regular water from tap. It doesnt seem to be growing. I added some fish water will see what happens. I wonder what seasol will do if added

Apparently a bucket with some cow manure in it makes great duck weed.

I peed in one of my tubs and the duckweed seemed to take off
My tubs are standalone and not connected to any system