Azolla the little fern that could

I've been growing this azolla (Azolla pinnata) since at least 2016.  It has been growing with us through drought, flood, snow, frosts, dust storms, and utter neglect.  

Remember that children's story of 'the little engine that could'?  It was a little train that kept going and going and going and when the hill got too steep it just kept going.  Azolla is like the plant version of this.  Very few plants have as many uses as azolla, and very few things are as simple to grow without posing a weed threat.

Azolla is simple to grow, incredibly productive (hence its ability to survive neglect), and I use it for a surprising number of things.  Very few plants have as many uses as azolla, very few plants are as simple to grow as azolla, an added bonus is this species is native to my area. 

While a few containers of azolla tucked under things around the yard can be surprisingly productive, each year I wish I had more azolla.  I consider increasing the amount I grow, but the reality of space and water constraints hits me and I only find space for a few more small containers of azolla. 

Azolla covering the water surface and forming a mat

Even though it doesn't look like a typical fern, azolla is a fern.  This little fern tends to float on the water surface with short thin roots dangling freely in the water, and does not ever need to touch soil.  Unlike many water plants, azolla can thrive in low nutrient water.  It is surprisingly resilient.  This species of azolla is native to Australia (and parts of Africa, and parts of Asia), and is the most common species of Azolla that can be found in my area.  

Azolla has a myriad of uses including animal feed, human food, mosquito control, fertiliser, mulch and compost, clearing water, providing honey bees somewhere to safely collect water, and plenty of other things.  I have eaten azolla, it isn't my favourite but in a pinch I guess I could eat it, that being said I would prefer to feed it to my chickens and then eat their eggs.  

If you ever have time to kill, look up the 'Azolla event'.  This is a time in the Eocene era were it is hypothesized that azolla growing in the arctic grew so much that it took so much carbon from the atmosphere that it changed the climate and caused an ice age.  Given that azolla can easily drawdown over 1.5 kg/m2/yr of carbon (some sources state it draws down 6.2 to 7.8kg per square meter), and the basin it was growing in covered around 4 million square kilometers, this hypothesis is plausible.  Sadly azolla will never be able to do this again, as the conditions that lead to this were rather unique, but it is fascinating nonetheless. 

Azolla and a rice plant

Azolla has a mutually beneficial symbiotic relationship with a blue green algae (cyanobacteria) called Anabaena azollae.  This is one of the few instances of symbiosis in nature being beneficial to both species.  To simplify what happens, the Azolla grows special little pockets to house the cyanobacterium and feeds it carbon, in return the blue green algae collects nitrogen from the air and turns it into a form that is usable by the fern.  Collecting nitrogen from the atmosphere like this is what makes azolla so useful. 

Not only is it rather rare to see mutually beneficial symbiosis, but this symbiosis is passed on from generation to generation and does not require re-inoculation.  To quote the Azolla foundation "we know of no other symbiotic relationship in which a cyanobacterium and plant pass down together during reproduction from generation to generation".  

Azolla also has a few other species of symbionts.  At this stage we don't really understand the purpose of those other species, or how they each interact, or if each is passed on or needs to be re-inoculated each generation.  It doesn't really matter too much, what matters is the azolla has various symbionts, and together they do a great job.  

Azolla and Chinese water chestnuts

I tend to grow azolla with aquatic vegetables such as Chinese water chestnuts.  I add some azolla when I plant them, and ignore it while it does its own thing.  Within a short amount of time the azolla covers the surface of the water.  From there it doesn't take too long to make a dense mat, which prevents mosquito larvae from being able to emerge and turn into adults.  

The azolla on top of the water surface also helps shade and cool the water, and somehow prevents the water from becoming too acidic.  Small containers can overheat in summer due to their small size, shading the water and shading the submerged soil helps keep the roots cooler which helps things grow better in the heat of summer.  

Azolla with watercress and brahmi

The mat of azolla also effectively blocks light.  This prevents algae from being a problem, and tends to prevent weed seeds from germinating.  

After the azolla turns into a thick mat, it starts to self compost.  New azolla grows on top, while the ferns underneath get smothered, and die.  This releases nitrogen and other nutrients that can be used by the water vegetables.  This works well as a natural organic biofertiliser.  This beneficial relationship between azolla and water plants was noticed hundreds of years ago, and azolla was introduced into rice paddies to increase rice yields and feed countless people long before the invent of chemical fertilisers.

The below container was partly filled with leaf litter, planted with a duck potato, topped up with water, and azolla added.  The soil level is too high, so there was not much space for water, but the azolla didn't mind, it grew well and covered the surface.  You can see the duck potatoes grew into large plants even though they were growing in small containers.  

Azolla and duck potatoes

The roots of azolla hang down in the water, and a myriad of life swims among them.  I don't know how these tiny things find their way into my containers, but I know if I look closely (or use a microscope) the roots are absolutely teeming with life.  

Tremendous amounts of research have been conducted into azolla.  All of this research points to azolla's productivity and ability to reduce the need for both chemical fertilisers and herbicides.  

While azolla is widely used as a biofertiliser in China and various other countries, it has not gained popularity in the Western countries where it is preferred to apply chemical fertilisers.  For backyard growers, azolla creates free organic fertiliser and free chicken feed.

Chinese water chestnuts growing in buckets with azolla

I start small aquatic vegetables in small pots of soil, then I transplant them into larger pots.  The ones in the photo below are in 10cm pots of soil submerged in a 4 liter ice cream container.  The azolla shades the water, which helps with temperature regulation and prevents algae from growing. 

Sometimes I place cuttings between these submerged pots.  The pots help hold the cuttings upright, keeping the base of the cutting under water, while the leaves remain in the air.  The azolla shades the water, prevents algae growth, and keeps the water cooler.  

Azolla with aquatic vegetables and cuttings

Recently I started to grow black forbidden rice (Oryza sativa).  I have some of the rice plants growing in pots of soil and being watered like any other vegetable plant, and some plants are in pots of soil submerged in shallow water.  I am curious to see which will perform better for me. 

In many countries azolla is intentionally added to flooded rice paddies.  Adding azolla is said to increase rice yields anywhere from 6.2% to 112% depending on which paper you read and what they are comparing.  All the research indicates that azolla helps rice plants grow larger, tiller more, and produce more grain (both in terms of weight as well as number of grains) per plant.  

I added azolla to most of the submerged rice I am growing.  It doesn't take long before the entire surface is covered.  Once the surface is covered it doesn't take long until the azolla forms a dense mat and starts to break down.  This should fertilise my plants, and provide food for numerous tiny water critters.  If nothing else, azolla will prevent mosquitoes from successfully breeding in these containers of still water.  

Newly planted Black forbidden rice with azolla

Azolla and rice - a few days later

The growth rate of azolla is pretty extraordinary.  

I took the photo below not long after adding azolla to the surface of the water.  You can see, the azolla is dividing and growing well. 

Black forbidden rice growing with azolla

I took the next photo of the same plants just six days later.  At this point the azolla had almost covered the surface of the water.  

This was towards the end of spring, over summer when the temperature is a little warmer the growth rate of azolla can be even faster.  

The rice plants seem to be doing well with azolla on the surface.  I am also growing a few rice plants in shallow water with no azolla to see if there is any noticeable difference.  I am taking photos and plan to write another blog post on this towards the end of the season.  While it is too early to make a call, at this stage the rice with azolla appears to be larger and more lush.

Six days of azolla growth

Azolla grows best floating on the surface of water, where it can double its biomass every few days.  Strangely enough, azolla can also grow long term on soil.  

Once I watered a pot using water that had a small piece of azolla in it.  The azolla sat on the surface of the soil and didn't die, and I decided to leave it and see what happened.  It stayed green and looked healthy enough.  

Over time the azolla grew, and slowly covered much of the soil surface.  This has not grown anywhere near as fast as when it is in water, but it has survived spring, summer, autumn, winter, another spring and is heading into its second summer.  This is long term survival.  

The azolla on top is growing, while the lower levels are mulching down.  The photos below are of the same pot of azolla, taken several months apart.  The first photo was taken after the azolla had been growing on soil for several months, the second photo was taken a few months after that. 

Azolla growing on soil long term

The same azolla still growing on just soil

From what I have seen, if growing on soil long term the azolla is a little tricky to get started, but once it gets established it is relatively hardy.  

The azolla needs damp soil and some shade to get started.  If I start by using free floating azolla and place it on soil it struggles.  If I get azolla that has started to form a dense mat, this seems hardier and tends to adapt to soil faster.  Once the azolla has been on soil for a while it changes slightly, it gets thicker and the roots change, and it seems to survive drier conditions and more sun.  

Interestingly, if I float some soil grown azolla on water, it seems to take some time to revert back to aquatic life.  For some time it just floats, it gets thinner, and does not divide.  Once it gets used to living on water, it then grows and divides like normal. 

Azolla growing on soil underneath dryland rice

As well as being excellent fertiliser, and great animal feed, azolla has a few other uses.  Honey bees and other small things need water in summer, but they can't always access water without drowning.  The bees can safely walk on azolla, and reach the water between the plants.  

Every summer I see a lot of bees on the azolla collecting water.  I also see butterflies standing on the azolla collecting water in the heat of summer.  

Dragonflies and other beneficial insects are also commonly seen around my azolla.  I am not sure if they are breeding in the water under the azolla, or if they are attracted due to the other insects, or if they are there for some other reason.  

Dragonflies are pretty, plus they are useful to have in my yard as they eat a lot of mosquitoes.  Whatever the correlation is between dragonflies and azolla, I am glad they are here.

Honey bee collecting water from azolla

Honey bee collecting water from azolla

For me, azolla performs best in part shade.  It certainly survives in full sun, but I find it grows faster when it has some shade.  Not surprisingly, being a plant means having too much shade will stop azolla from growing well. 

Azolla turns red when it is stressed.  This stress can be from too much sun, or from extreme temperatures.  When azolla is red, it grows slower, and is meant to be less nutritious.  While a pond covered in bright red azolla is a pretty amazing thing to see, I prefer to keep mine green and growing fast so I can use more of it for various things.  This normally means giving it a little shade.

Azolla starting to turn red from stress

Azolla and duckweed

Azolla spreads and divides fast.  It can double every day or so under good conditions.  

While azolla also reproduces sexually and produces spores like other ferns, the main way it reproduces is asexually.  Any part of azolla that breaks off has the potential to produce more azolla.  

While azolla prefers not to be frozen over winter, my azolla survives heavy frost, and has survived being frozen for days on end.  If it ever died from the cold, I have little doubt that either a tiny part was still alive, or sporocarps could be present in the water, and it could recolonise pretty quickly once the weather warmed.  

Azolla makes great chicken feed

I use azolla to supplement chicken feed, this helps the chickens stay healthy, and it lowers the feed bill.  

Azolla is surprisingly nutritious, and it is readily eaten by my hens.  As mentioned earlier the roots of azolla are teeming with tiny life, when my chickens eat azolla they also eat these tiny invertebrates.  

Studies indicate that azolla can replace up to 20% of bought food for layer hens without seeing a decline in eggs, but I can't grow that much azolla here.  I give them as much as I can as it replaces some bought food, and lowers the cost of eggs a little bit.  

Azolla is appreciated by hens over summer when there isn't much grass or other greenery available.  I can either float azolla on water, or I can scoop it into a dish, either way my hens eat it pretty quickly.  

Azolla and rice plants

While I am a little disappointed that azolla will never again be responsible for creating an ice age, I still like azolla.  I tend to find a lot of uses for azolla, and could use it a whole lot more if I had more of it.  I have to be content only growing a little bit as I don't have a lot of extra space.  

If you grow any animal feed, or have a garden, or grow water plants, or want to provide somewhere safe for honey bees to collect water, then azolla is for you.  Once you get azolla, you never need to buy it again as you can keep it going forever.  You may be able to find some azolla locally, or you may need to buy it.  You only need a little to get started as it divides fast.  Very few places other than dedicated water garden nurseries seem to sell azolla.  If you can't find any locally, I sell azolla through my for sale page.  

Azolla and Chinese water chestnuts growing in a bucket