Azolla spp.
mosquito ferns
Worldwide temperate and tropical fresh waters
Container Friendly
Native to North America
Overview
Azolla spp. is a genus of six or seven species of tiny floating aquatic ferns in the family Salviniaceae, found on still and slow fresh water across warm and temperate regions worldwide. Individual plants are only 0.4-1 in (1-2.5 cm) across, with branching stems clothed in overlapping scale-like leaves, and trailing roots that hang into the water. The plants float in dense mats on ponds, ditches, and rice fields, green in shade but flushing red or purple in strong sun or cold. Each leaf has a cavity housing the nitrogen-fixing cyanobacterium Anabaena azollae, a partnership that lets the fern draw nitrogen from the air and grow rapidly even in nutrient-poor water. Reproduction is mainly by fragmentation, with spores produced in small cases beneath the plant. The genus occurs on every continent except Antarctica. Because of the nitrogen it captures, Azolla spp. is grown as a green manure and livestock feed, especially in rice farming. Free growth can cover a water surface completely, cutting light and oxygen to the water below, and several species are invasive outside their native range.
Native Range
Species are spread across temperate and tropical fresh waters worldwide, on every continent except Antarctica. Plants float on still or slow water in ponds, lakes, ditches, marshes, and flooded fields.Suggested Uses
Grown on rice paddies and farm ponds as a nitrogen-fixing green manure and as feed for poultry, fish, and livestock. In water gardens it is used as a quick floating cover for shade and to limit algae, where its spread can be contained.How to Identify
Appearance
Size & Dimensions
Height1" - 1"
Width/Spread1" - 1"
Bloom Information
As a fern, Azolla spp. produces no flowers. It spreads mainly by breaking apart, with each fragment growing into a new plant, and reproduces sexually through spores formed in small cases on the underside. Mat growth is fastest in warm, still, sunlit water.
Detailed Descriptions
Foliage Description
green, turning red or purple in sun or coldGrowing Conditions
Sun Requirements
Requires 4-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Plants float on still or slow fresh water in full sun to part shade and need no soil or planting. Growth is fastest in warm water and slows or dies back in cold, with surface mats often reddening before winter. The nitrogen-fixing partner removes any need for feeding, and plants multiply quickly where nutrients and warmth allow. Mats can double in size within days and may need regular thinning to keep open water. Hard frost kills the floating plants, though some overwinter as sunken fragments or spores. Movement of plant material between waters spreads the fern readily, including into places where it is unwanted.Pruning
Excess mat is skimmed off the surface with a net or rake to keep part of the water open and maintain oxygen levels. Removed material composts quickly and is used as a nitrogen-rich mulch.Container Growing
✓ Suitable for container growing