TankBud

Fairy moss

Azolla filiculoides

Also known as Water fern, Mosquito fern, Red azolla, Pacific azolla

FreshwaterFloatingFragmentationDivision

Fairy moss (Azolla filiculoides)
Len Worthington · CC BY-SA 2.0

Care at a glance

Light
Medium light
CO2
No CO₂ needed
Temperature
59–82°F
15–28°C
Max height
0.8 in
2 cm
Growth rate
Fast
Placement
Floating
Type
Floating
pH
6.0–7.5
Hardness
2–18 dGH
Spread
11.8 in (30 cm)
Nutrient uptake
Water column
Growth region
Submersed or emersed
Difficulty
Easy
Family
Salviniaceae
Origin
A tiny floating fern native to warm and temperate fresh water across the Americas, now naturalized widely on ponds, ditches, and still backwaters.

Overview

Fairy moss is a minute floating fern whose overlapping, scale-like leaves form a soft green film across the water. It is easy to grow.

Did you know

Azolla has been grown for centuries as a natural fertilizer in flooded rice paddies, because its cyanobacterium pulls nitrogen from the air.

Caring for fairy moss

Drop fairy moss on the surface, and it spreads quickly with no planting needed. It dislikes strong surface agitation, so calm water and a gentle filter outflow suit it best.

Moderate light is enough, and it needs no CO2. Under strong light or in cool weather, the mat turns deep red. It draws nutrients straight from the water, so a liquid fertilizer feeds it, and that uptake helps starve out algae. It grows at 59 to 82°F (15 to 28°C).

It multiplies fast, since pieces that break off keep growing. Scoop some out every week to keep it from covering the whole top. Left in place, the mat gives fry and shrimp shade and cover at the surface.

Good to know

Fairy moss is a true fern, not a flowering plant, and it spreads by spores as well as by breaking apart. Each frond houses the nitrogen-fixing cyanobacterium Anabaena azollae in a small leaf cavity. That partnership passes from one plant generation to the next.

In the wild

Fairy moss is native to warm and temperate fresh water across the Americas. It is now naturalized widely on ponds, ditches and still backwaters. Parts of Europe ban its sale as an invasive weed.

Common questions

Does fairy moss need to be planted in the substrate?

No. Fairy moss floats at the surface and takes its nutrients straight from the water.

Does fairy moss need CO2?

No. Fairy moss grows well without added CO2.

How much light does fairy moss need?

Fairy moss wants medium light. A light sold for planted tanks covers it.

How do you propagate fairy moss?

Fairy moss propagates by fragmentation and division. Pieces that break off keep growing, so pulling a clump apart spreads it. Each plant buds off new ones, so a few soon cover the surface.

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