Azolla filiculoides is the perfect aquatic plant for adding texture to small ornamental ponds or water gardens. This adorable free-floating fern is commonly known as mosquito fern, water velvet, water fern, or fairy moss. It is classified under Salviniaceae, a small family of about 20 heterosporous ferns with an aquatic habit.
These differ from other ferns not just because they don’t have the typical appearance of fronds, but also because they produce 2 different spore types: microspores and megaspores. These develop into either male or female reproductive parts, making these species more similar to seed-bearing plants.
Native to the Americas, fairy moss is easily introduced into new water systems because of its relatively small size. It is now naturalized in freshwater systems all over the world. This fern actually has both exposed and submerged parts. The bright green upper leaves resemble those of cedar trees and stay afloat on the water’s surface. When exposed to full sunlight conditions, these leaves tend to become more reddish or purple in color!
A submerged set of lower leaves arise from a short stem, which terminates in a set of feathery roots. These remain suspended close to the water’s surface as the plant grows to just 3 inches (7 cm) at maturity. A single fairy moss can keep producing leaflets and spread to an indefinite width.
Facts, Benefits & Uses of Fairy Moss
The roots of fairy moss are able to take up nutrients directly from the topmost sections of the water column. In contrast, the leaves have a symbiotic relationship with cyanobacteria and are able to take up nitrogen from the atmosphere.
When nutrient levels are high and sunlight is abundant, this species has the tendency to produce expansive mats. These can thicken and spread wide enough to fully cover the water’s surface, preventing light from penetrating into the lower depths of even shallow water bodies. Don’t hastily dismiss fairy moss, however, as it can provide many vital environmental services too.
When fairy moss mats are regularly maintained, they can help prevent the growth of algae and ensure that your pond water remains clear. Light mats may also aid in reducing water evaporation rates and maintaining water temperatures throughout the hottest months. Moreover, the plant’s submerged structures are able to provide protection and refuge for small aquatic animals.
Apart from these benefits, fairy moss has decorative value as well. A sparse cover of the purple-tinged foliage can be quite eye-catching. The rich texture of the overlapping leaflets may agreeably contrast the smooth surface of clear water. Anyone with a keen sense for design will quickly see the appeal of this species!
Fairy Moss Growth, Hardiness & Climate
Availability of phosphorus, rather than nitrogen, can significantly affect the growth of fairy moss. When phosphorus concentrations are below optimal, the foliage of A. filiculoides has the tendency to produce less chlorophyll. This can prevent the plant from producing the energy stores required to develop standard-sized, durable organs. Moreover, nutrient deprivation can cause the plant to allocate more energy to root production.
Conversely, a surge of nutrients (particularly iron, calcium, phosphorus, and potassium) could cause fairy moss populations to grow extremely vigorously. In areas where populations are exposed to fertilizer run-off, mats can become thick and cause the underlying water layers to become anoxic. If nutrient concentrations in your pond or water feature are not optimized, you may have to dedicate more time and resources to managing fairy bloom populations.
How to Plant Fairy Moss
Growing and propagating this species is as easy as 1-2-3! It won’t even require a “planting” step, in the usual sense, as it does not spread via seed or require soil. Simply obtain intact cuttings from your local plant center or aquarium shop. To ensure that the cuttings are able to establish themselves in your pond, all major plant organs should be intact. Ideally, the individual floaters should have shoot and root systems that aren’t too fragile to the touch.
Gently place your fairy moss plants on the water’s surface and make sure that the upper leaves are able to stay upright. This should be done during late spring or summer, when young plants can establish themselves in relatively warm water. They should gradually produce more leaflets and readily spread if nutrients are available.
If you have herbivorous fish and only a few small individuals of fairy moss, you may have to separate the plants or restrict them to shallow pond edges where they are less likely to be grazed upon. This should be done at least until the population is large enough to sustain grazing.
How to Care for Fairy Moss
Fairy moss can be quite demanding when it comes to maintenance, especially if your populations have begun to form mats. You may have to periodically scoop out portions of growth with the use of a net. This won’t affect the remaining populations and this would help prevent submerged plants from being light-deprived. To prevent clusters from overgrowing specific areas of your pond, you can separate them and redistribute them to other areas.
Fairy moss is generally pest-free and disease-resistant. As long as adequate sunlight is provided, the fronds can withstand a wide range of ambient conditions. Do keep an eye out for decaying plants or leaf matter that become trapped under the fairy moss mats. These may reduce oxygen levels and attract bacteria as they decompose.
How to Winter Fairy Moss
Fairy moss is a frost-tender fern. Its delicate fronds are unable to tolerate freezing conditions. It will survive outdoors only if located in USDA hardiness zones 8 – 11, where winters are generally warm. Even if frosts don’t occur in your area, lowered temperatures signal the plant to enter a phase of dormancy. This species produces dormant “buds” that sink to the pond bottom towards the end of fall. Once temperatures increase in spring, the buds begin to sprout and float back toward the surface.
If located outside of these zones (in areas that experience harsher winters), it is advisable to overwinter your fairy moss indoors. You won’t have to take in entire mats, of course – a few individually selected plants should quickly spread outdoors in the succeeding spring and summer months. Select the best-looking fronds and place these in a temperature-regulated indoor aquarium. You can also use a container of water placed in the warmest corner of your greenhouse (though the fronds may die back or grow dormant if temperatures drop considerably).
If you elect to overwinter your plant indoors, make sure to transfer them before the first frost occurs. Remove any other fairy moss colonies that you don’t intend to keep. Avoid letting these die back in your pond as any decomposing parts can attract pathogens.
Is Fairy Moss Invasive or Toxic?
Fairy moss is not known for carrying any toxic compounds, but it can definitely spell trouble in another way! When mismanaged or left to spread profusely in nutrient-rich water, its mats can become very thick and dense. They can become a somewhat impregnable physical barrier between water and air, preventing even mosquitoes from laying their eggs. This is why this species is also frequently called mosquito fern.
Due to its mat-forming habit and tendency to outperform native plants, Azolla filiculoides has become invasive in several countries. It is now considered an illegal non-native plant in some parts of the UK, where it is banned from being distributed or sold. Mechanical, chemical, and biological means of control have been employed in sites that have been infested with this fairy moss. The most effective type of control has so far been the use of weevils in South Africa. So proficient at decimating fairy weed mats, these insects can cause the plant to become locally extinct!
Is Fairy Moss Edible? Will Fish Eat it?
It’s completely safe for pond fish, such as koi and goldfish, to occasionally nibble on fairy weed fronds. In fact, your herbivorous pond inhabitants can help you manage the spread and thickness of your fairy weed mats.
This species is actually well-researched for its nutritional content, and is considered a potential ‘super food’ for livestock! It is rich in protein, vitamins, and minerals and can easily be farmed for consumption.
Where to Buy Fairy Moss & Seeds? (UK & US)
Azolla filiculoides can be purchased from aquascaping shops and plant nurseries that carry aquatic plants. Online stores tend to carry this plant as well, and will likely ship out containers with a small amount of water to keep a few individuals hydrated on their journey to you. Before making your purchase, make sure that this species isn’t banned from being cultivated or distributed in your area.
