Azolla Caroliniana care guide
Azolla Caroliniana (Azolla caroliniana) — medium light, 15-28 °C, pH 5.5-7.5, no CO2.
Compiled by Aquairi from published sources · Published · Updated
Overview
Azolla Caroliniana (Azolla caroliniana) is a scale-leaved liverwort of the family Salviniaceae, grown as an aquarium plant. A tiny floating fern that forms dense green carpets on the water surface, turning reddish under intense light. Contains symbiotic nitrogen-fixing cyanobacteria, making it a natural fertilizer for the aquarium.
Taxonomy
- Family: Salviniaceae
- Genus: Azolla
- Scientific name: Azolla caroliniana
- Common synonyms: Mosquito Fern, Fairy Moss
Habitat
Azolla caroliniana originates from North America, where it grows in freshwater marshes, ditches and slow-moving streams, frequently emersed on seasonally flooded ground.
Growth requirements
- Lighting: medium
- CO2: not required
- Temperature: 15-28 °C (59-82 °F)
- pH: 5.5-7.5
- GH: 2-12 °dGH
- Substrate: none (floating or epiphytic)
- Maximum height: 2 cm
- Growth rate: fast
- Nutrient demand: low
- Recommended placement: floating
- Typical trim interval: 7 days
Placement
In aquascapes this plant floats at the surface.
Propagation
Propagation is by division of the parent clump; daughter plants are separated once they have formed several leaves and visible roots.
Common issues
Pale or stunted new growth usually signals a nutrient or iron deficiency, while algae on older leaves often follows light that exceeds the available nutrients or CO2; correcting fertilisation and trimming affected parts resolves most cases.
Propagating Azolla caroliniana (Carolina Mosquito Fern)
Overview
Azolla caroliniana is a tiny floating fern with scale-like fronds 5–10 mm long that form dense mats up to about 4 cm thick. Fronds are green to reddish, turning red most often in winter and under strong light, and microscopic trichomes give the surface a water-repellent, velvet-like texture. It fixes nitrogen from the air through symbiotic cyanobacteria, which is why it is used as a biofertilizer in rice culture and acts as a natural fertilizer in the tank.
Propagation Method
Azolla propagates vegetatively by division: the mat branches and fragments break off, each piece continuing to grow on its own. It spreads rapidly, so even small fragments quickly form new mats. No flowering or cuttings are involved — simply separating portions of the floating mat is enough.
Step-by-Step
- Scoop a healthy portion of green mat from the surface.
- Break it into smaller clumps, each with several connected fronds.
- Float each clump on calm water with space to expand.
- Keep surface agitation low so the tiny fronds are not pushed together or sunk.
- Harvest and re-divide regularly as the mat doubles to keep portions vigorous.
Conditions for Healthy Growth
Azolla grows best with medium light and calm water. It tolerates a wide range, surviving water near 5 °C in winter with optimum summer growth around 25–30 °C. No CO2 or substrate is needed; its nitrogen-fixing symbiont lets it thrive even in low-nutrient water.
Maintenance
Because the mat doubles quickly and can reach several centimeters thick, scoop out excess regularly to keep light reaching plants below. A dense Azolla layer suppresses other growth, so steady thinning is the main routine task.
Common Challenges
The main challenge is overgrowth: the fast-doubling mat can fully cover the surface and shade plants underneath. Excessive surface flow can break up and damage the delicate fronds.