Fairy Moss Care Guide – Planting, Growing, and Propagation

Fairy Moss (Azolla) Care Guide – Planting, Growing, and Propagation

Azolla (also called Fairy moss or Mosquito fern) is a stunning, prolific, and hardy aquatic fern often employed by hobbyists in decorating their freshwater aquaria, paludaria, and ponds.

This species adds a great deal of texture and depth to the aquarium, and it improves the overall aesthetical value with its velvety appearance and impressive bright green/reddish coloration.

Fairy moss is endowed with rapid growth and amazing propagative qualities, and it can also withstand a wide range of temperatures and pH levels.

Do you know that this plant also caused Ice age on the planet?

Keep reading for everything there is to know about the Fairy moss; including its nature, preferred water conditions, as well as how to cultivate and care for the plant in an aquarium, and other interesting facts.

Quick Notes about Fairy Moss

Common Name Fairy moss
Other Names Mosquito fern, Water fern, Water velvet, or Red water fern
Scientific Name
Azolla spp.
Difficulty Easy to Medium
Lighting Medium 
Optimal pH 6.0 – 7.5
Optimal GH 2 – 18 
Optimal Temperature 68 – 77 °F (20 – 25 °C)
Substrate Not needed
Can float:
Growth Rate Extremely fast
Placement in Tank
Fronds (leaves) up 0.4 inches (~1 cm)
Not needed to low
CO2 Not needed
Propagation Through spore formation or by splitting 

Origin of Fairy Moss

Azolla spp., commonly known as Fairy moss is a genus of about 7 prolific, floating aquatic ferns in the family Salviniaceae.

Two species from this genus are popular ornamental pond plants; these are Azolla filiculoides & Azolla cristata (formerly known as Azolla craroliniana).

Azolla spp. is native to the Americas, and the extant species are considered as weeds and non-native plants in wetlands, ponds, ditches, freshwater lakes and streams.

Fairy moss features a diminutive form, small leaves, plus fast-growing and reproductive habits similar to the renowned aquarium/pond plant: Duckweed.

Habitat of Fairy Moss

Fairy moss is native to warm temperate and tropical regions of the Americas, from the Southeastern United States to Central & South America.

This aquatic fern has been introduced to other parts of the world, including Asia, Australia, and the United Kingdom.

Fairy moss is commonly found in shallow, still freshwaters where it forms extensive intense green or reddish mats on the surface of the water.

Description of Fairy Moss

Fairy Moss Care Guide – Planting, Growing, and Propagation (Azolla caroliniana)
Azolla caroliniana

Fairy moss is a miniature, short-stemmed, heterosporous, aquatic fern with tiny green to reddish scale-like fronds that overlap each other.

The fronds of fairy moss are typically less than 1 cm (0.4 inches) long, and they are covered in tiny epidermal protuberances called trichromes. These trichromes are unicellular in Azolla filiculoides and multicellular in Azolla cristata.

Fairy moss floats on the water surface by means of the numerous, tiny closely overlapping fronds that contain tiny gas bubbles.

Fairy moss grows rapidly and thrives in the abundance of essential nutrients especially phosphorus. Under full sunlight exposure, the fern’s fronds assume an intense reddish colouration.

This invasive plant is rich in protein, amino acids, vitamins, and minerals, thus making it an excellent livestock feed.

In addition, fairy moss has great phytoremediation qualities — it is able to effectively remove heavy metals such as copper, zinc, arsenic, lead, chromium, aluminum, and nickel from the water.

That’s not all, Fairy moss can also be used as a bio-fertilizer in paddy fields because of its ability to fix nitrogen from the air.

Fairy moss is dubbed “mosquito fern” as it can be used to control mosquito larvae in paddies. The aquatic fern forms dense mats on the surface of the water, and these mats tend to prevent mosquitoes from laying eggs in the water.

Symbiotic Relationship with Cyanobacteria

Fairy moss is capable of fixing atmospheric nitrogen. Basically, this plant can grow in aquatic environments almost devoid of combined nitrogen if there is enough phosphorus.

This is possible since the aquatic fern is in a symbiotic relationship with the cyanobacterium Anabaena azollae that lives in the dorsal lobe cavity of its leaf. In its turn, the plantprovides the cyanobacteria with a safe environment for growth and multiplication.

Due to this extraordinary ability, the aquatic fern grows and propagates very fast, doubling in biomass every few days.

Note: In fact, phosphorus is for Azolla, as for many other plants, the limiting nutrient for growth.

Interesting fact: Do you not that scientists believe that Azolla with its symbiotic relationship with cyanobacteria caused Ice Age? Around 50 million years ago, this plant covered the entire Arctic Ocean and took advantage of the abundant nitrogen and carbon dioxide. A succession of ice ages was triggered once the atmosphere’s CO2 dropped below 600 ppm around 2.6 million years ago.

Tank Requirements and Water Parameters

Tank size:

Fairy moss can be grown in a freshwater tank of at least 10 gallons (~40 L).

However, larger tanks and ponds are more suitable for cultivating this aquatic fern due to its rapid growth and spreading ability once established.

Water type, Temperature, Hardness, and pH:

Temperature: The optimal temperature for growing Fairy moss is between the range 20 – 25 °C (68 – 77 °F). Nevertheless, this species can withstand a wide range of temperatures, from 5 °C (41 °F) to as high as 45 °C (113 °F).

Cold temperatures (−4°C and more) or prolonged freezing conditions during winter months cause the fern to die back, and this often results in the production of buds that submerge to the bottom of the water until the next season (spring).

pH: Fairy moss can survive in freshwater ponds and aquariums with pH levels between 4.5 – 8.0. The optimal growth rate is achieved at 6.0 – 7.5 pH.

Hardness: This fern thrives in soft to fairly hard water. In aquariums, between 4 – 18 dGH.

Brackish water: Azolla can grow in brackish water with low levels of salinity (>8.4 g/l). However, its tolerance to salinity has not been explored.


Fairy Moss (Azolla) Care Guide – Planting, Growing, and Propagation - redLighting is a strong requirement for optimal growth and development in this fern species.

When exposed to bright sunlight and elevated temperatures, the plant exhibits an exponential growth rate and its fronds take on an intense reddish coloration.

According to the study, the reddening of plants was a response to low temperature and high light conditions which could be prevented by shading. 

So it’s best to provide moderate to high lighting in your freshwater aquarium using high-quality LED lighting and make sure to maintain a standard photoperiod of 8 – 10 hours to encourage healthy growth and survival of your fairy moss.

Read more about it in my article “Advanced Guide to Planted Tank Lighting”.


The fern comes from shallow bodies of water with slow water movements. That said, be sure to avoid much surface agitation on the surface of the water in your fish tank to prevent rotting of the fronds.


It doesn’t matter since Fairy moss grows on the surface of the water.

CO2 and Nutrient Supplementation:

CO2: Fairy moss does not require CO2 to grow and thrive in the aquarium. As a floater, this plant gets enough from the air.

However, the presence of nutrient-rich water will help it grow healthy and vigorously.

Fertilizers: Thus, adding liquid fertilizers especially those rich in phosphorus, iron, and potassium will encourage healthy growth and vibrant coloration.

Also, keep in mind that having high nutrient concentrations in your aquarium water will cause the fern’s growth to explode, hence resulting in reduced oxygen levels due to the spread of thick mats on the water surface.

To this end, you need to aim for a middle ground between paucity and the overabundance of nutrients.

Important: If you keep shrimp in the tank with Fairy moss, I would highly recommend reading my articles:

The point is that a high level of CO2 and Copper (most fertilizers contain copper) is extremely dangerous to the shrimp.

Care and Maintenance of Fairy Moss

If I were to rank this aquatic fern in terms of care difficulty, I will go with easy to medium.

The reason being that Fairy moss grows and propagates very quickly and hence needs to be thinned on a regular basis.

Under optimal condition, the Fairy moss population expands rapidly, in fact 4 – 7 days is enough for its biomass to double in size, and the dense mats can easily overrun your tank.

Interesting fact: The aquatic fern Azolla is one of the fastest-growing nitrogen-fixing plants on Earth and therefore considered as a potential source of biomass for bioenergy production.

You just have to scoop out some of the overgrowths using a fishnet and discard them in a plastic bag. This will reduce the Fairy moss population and also restore light penetration to submerged plants in your freshwater aquarium.

It’s equally a good time to inspect for decaying fronds within the thick Fairy moss mats; make sure to clip and remove the fronds from the tank to prevent them from decaying further, depleting the oxygen levels, and ruining the aquarium water.

In addition, make sure to perform regular, partial water changes to maintain excellent water quality. Provide decent illumination and keep the water parameters at the ideal values to encourage optimal growth of your Fairy moss mats.

Planting and Propagation of Fairy Moss

Fairy moss is a floating aquatic fern. So the species can be grown in the aquarium/pond by spreading the individual plantlets on the water surface.

Planting should be done after thoroughly disinfecting in a bleach or potassium permanganate solution, rinsing in dechlorinated freshwater, and letting them to air-dry.

As usual, the specimens should possess well-defined shoot and root systems to be able to adapt and establish themselves easily in your aquarium or pond.

If you want, you may restrict Fairy moss to a given area of the aquarium by creating borders using an ideal aquascaping instrument. Once the plants are established in your aquarium, you may declutter extremely thick mats by thinning and redistributing some plants to sparse areas on the water surface if need be.

Moreover, be sure to provide gentle water flow in the fish tank to prevent surface splashing.

Fairy moss propagates:

  • sexually through spore formation (production of male & female spores: microspores & megaspores);
  • asexually by splitting or fragmentation of vegetative parts.

Problems Associated with Fairy Moss

Overcrowding: Fairy moss grows and spreads rapidly when optimal conditions and high nutrient levels are available. This aquatic fern can completely cover the surface of the aquarium in a short time after fully adapting to the tank’s conditions.

Unfortunately, this situation may spell doom for your aquarium because not only do the dense mats overcrowd the water surface, they equally block light penetration to submerged plants and reduce the oxygen content of the aquarium water significantly; thus capable of choking fish and other aquatic species within the enclosure.

Interesting fact: Fairy moss created such a thick mass that one sheep farmer in the Free State Province estimated losses of 40 sheep per year, which had drowned after walking into weed-infested dams perceiving them as pasture.

Solution: excess or overgrown foliage should be pruned frequently.

Leaf Rot: This problem is often caused by a high level of surface agitation in the aquarium.

Solution: Control water flow. The ideal condition for growing fairy moss should be slow or gentle water movements.

Benefits of Fairy Moss

Removal of excess nutrients:  Fairy moss is extremely effective at soaking up heavy metals from the water.

According to the study,  this plant can even remove low concentrations of copper.

Algae control: by reducing light beneath the water and consuming excess nutrients, Fairy moss also effectively reduces the growth of algae. 

Hiding place: This plant is a good hiding place for shrimp and small fish.

Foraging place: Acts as a buffet of biofilm, which is an ideal first food for newly hatched fry and shrimplets.

Prevents fish jumping: Once Fairy moss creates a thick mat and covers the surface, it will keep fish from jumping, when you do not have a lid. Just be careful with overgrowth! 

Animal food: Azolla is a very high protein food. According to the study, there is 23.8% crude protein in Azolla. Therefore, it can be used as a food source for fish, shrimp, snails, crayfish, crabs, etc. 

Note: Use a blender to mix it up with montmorillonite clay that acts as a binder. Spread it thinly over the surface and let it completely dry. Break it into small pieces and feed your fish or shrimp. They will like it!

Fairy Moss and Compatible Tankmates

Ideally, you need to choose species that can live in a shaded aquarium, or utilize the thick mats of fairy moss as a medium for egg spawning, or as a sanctuary and feeding station.

Avoid or Be Careful:

What about herbivorous like Koi fish, Goldfish, Texas cichlids, Front cichlids, Jack Dempsey, Red Devil, Oscars, and others?

These species may/will feast on the soft foliage of fairy moss, but that won’t be a problem since the fern can withstand grazing and it is also capable of doubling its biomass every few days.

Buying Fairy Moss

Fairy moss can be purchased from local fish stores, nurseries, and online stores.

A cup of fairy moss usually goes for $5 or less, and this contains many individual plantlets which may or may not be parasite-free — so make sure to disinfect thoroughly before planting them in your aquarium or pond.

Ideally, the specimens should be healthy-looking and brightly colored, and the shoot and root systems should be intact to enable them to adapt, grow and thrive in a new environment.

Quarantine Fairy Moss

Unless you are completely sure that the plant is safe, do not forget to quarantine and disinfect Fairy moss to avoid the risk of contamination.

  • The plant can have parasites, and hitchhikers like pest snails, or even predators (dragonfly, damsefly nymphs, etc.).
  • It could also be treated with chemicals (pesticide) to remove parasites, snails, etc. However, these chemicals are extremely poisonous to fish, shrimp, and other invertebrates.

To find out more, read my articles:  

How to Remove Snails from a Shrimp Tank.
How to Quarantine and Disinfect Aquarium Plants.
Pesticides in Shrimp Tanks. Plants Quarantine.

In Conclusion

Fairy moss is a common, heterosporous, free-floating fern suitable for adorning freshwater tanks and ponds.

The plant features tiny, attractive fronds that are brightly green/reddish colored and they contain the blue-green alga Anabaena azollae which is capable of fixing atmospheric nitrogen, thus enriching the water. Also, the thick canopy formed by fairy moss beautifies the surface of aquariums and ponds and provides ample shade/cover for aquatic critters.

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