Simply scoop the excess plants off the water surface with a net.

Plant guide

Water fern.

Azolla filiculoides

Pronounced uh-ZOH-luh fil-ih-koy-DEEZ

Also known as Floating Fern, Pacific azolla, Pacific azolla, Pacific mosquitofern, Pacific mosquito fern, Pacific mosquitofern, Red Fern, Water Fern, Water Fern, Fairy moss

water fern — Photo by Kevin Thiele (CC BY) via iNaturalist

This tiny floating aquatic fern is a fascinating plant that forms dense mats on the water surface. It is well known for its symbiotic relationship with nitrogen fixing cyanobacteria. You will often see it turning reddish in cooler weather or high light.

Another photo of Water fern — Photo by Ong Jyh Seng (CC BY-SA) via iNaturalist

At a glance

Care level: Easy
Plant type: Aquatic fern
Light: Full sun to partial shade
Indoor light: Bright indirect
Water: Every 0 days
Mature size: 1 to 2 centimeters
Growth rate: Fast
Hardiness: USDA 7 to 10

Care

Keep this plant in a calm body of water with plenty of sunlight. Watch for rapid spread, as it can quickly cover an entire pond surface if left unchecked. Ensure it stays moist at all times since it is strictly aquatic.

Watering: This plant must remain floating in water at all times.
Feeding: Usually obtains nutrients from the water, but a light liquid aquatic fertilizer helps in nutrient poor ponds.
Pruning: Scoop out excess plants to prevent them from completely covering the water surface.
Repotting: This is a free floating plant and does not require potting.
Soil: None, aquatic
Soil pH: 6.0 to 8.0
Temperature: 0 to 30°C
Humidity: 70 to 100%

Safety

People: There is no evidence of human toxicity, but it should not be eaten due to potential water contamination.
Children: Keep away from small children as it can be a choking hazard if ingested from water features.
Edibility: This plant is not intended for human consumption and may accumulate heavy metals from water.

How to identify it

Tiny triangular overlapping leaves
Floating on water surface
Roots hang directly into water
Color shifts green to red

Height: 0.01 to 0.02m
Spread: 0.1 to 10m
Leaves: green, red, deciduous
Flowers: 0cm

Problems to watch for

Overgrowth · It can quickly cover the entire surface of a pond, blocking light and oxygen.

By symptom

Plant problems by symptom

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Growing it

Propagation: division
When to plant: spring, summer

Use this plant to shade out algae in small ponds.

Grows well with

Water Hyacinth · They both thrive in similar aquatic conditions.

Similar species

Duckweed · It is a similar floating plant often found in the same habitats.

Science

Family: Salviniaceae
Genus: Azolla
Order: Salviniales
Class: Polypodiopsida
Native range: Americas
Conservation: It is considered an invasive species in many parts of the world outside its native range.

It floats on the water surface and thrives in nutrient rich, still, or slow moving water.

Value to wildlife: provides cover for aquatic insects, habitat for small fish
Uses: water garden cover, natural fertilizer, aquarium plant

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 1/9
Soil reaction: 5/9
Light: 7/9
Temperature: 6/9
Moisture: 9/9
Nutrients: 7/9

Taxonomy resolved against GBIF.

Questions people ask

Is it a moss?: No, it is a tiny aquatic fern.
How do I control it?: Simply scoop the excess plants off the water surface with a net.

Where the name comes from

The name Azolla comes from the Greek words for dry and to destroy, referring to its tendency to die when dried out.

Good to know

It is often called fairy moss.
The plant turns reddish in bright sun or cold temperatures.
It is one of the fastest growing plants on earth.

Keep your water fern growing

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This guide was generated with AI on September 26, 2026 and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.