Fairy moss

Azolla filiculoides

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

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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

Drop it on the surface in moderate light and it will spread quickly with no CO2 or planting needed. It dislikes strong surface agitation, so calm water and a gentle filter outflow suit it best, and weekly scooping keeps it from covering the whole top. It draws nutrients straight from the water, which helps starve out algae.

In the wild

Azolla is a minute floating fern whose overlapping scale like leaves form a soft green film across the water surface. Under strong light or cool weather the mat turns deep red, giving it real ornamental appeal. It multiplies fast and provides shade and cover for fry and shrimp at the surface.

Good to know

Azolla is a true fern, not a flowering plant, and it spreads by spores and by simply breaking apart. Each frond houses the nitrogen fixing cyanobacterium Anabaena azollae in a small leaf cavity, a partnership carried from one plant generation to the next.

Did you know

Because its cyanobacterium pulls nitrogen from the air, Azolla has been grown for centuries as a natural fertilizer in flooded rice paddies, and it is banned from sale as an invasive weed in parts of Europe.