Water Fern – Rare

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Water ferns are a diverse group of aquatic plants, and their care can vary depending on the specific species. The most common “water fern” is a floating plant of the genus Azolla, often called mosquito fern or fairy moss. There are also submerged and semi-submerged water ferns, like Java fern (Microsorum pteropus) and African water fern (Bolbitis heudelotii), that are popular in aquariums.

Here is a general care guide for water ferns, with a focus on the most common types.

Water Fern (Azolla) Care (Floating Ferns)

Azolla is a free-floating fern that forms dense mats on the water’s surface. It’s known for its rapid growth and ability to fix nitrogen.

1. Water:

• Aquatic environment is a must. Azolla must be grown in water. It’s often used in ponds, water gardens, or large containers.
• High moisture and humidity: It requires a consistently moist habitat and is not tolerant of dry conditions.
• Still or slow-moving water: Azolla does best in calm water without strong currents or turbulence.

2. Sunlight:

• Full to partial sun. Azolla thrives in full sun, which promotes vigorous growth. It can tolerate partial sun, but growth may be slower.
• Too much sun can be a stressor. In very bright light or high temperatures, the foliage may turn a purplish-rose color.

3. Nutrients:

• Nutrient-rich water: Azolla needs a moderate level of nutrients to thrive, including nitrogen and phosphorus. It absorbs nutrients directly from the water.
• Symbiotic relationship: It has a unique relationship with a nitrogen-fixing cyanobacterium, which allows it to absorb atmospheric nitrogen, making it a natural fertilizer.
• Be careful with excess nutrients. High nutrient levels can lead to an explosion in growth, which can deplete oxygen and block sunlight for other aquatic life.

4. Maintenance:

• High maintenance for growth control: Because of its fast growth rate (it can double its size in a few days), Azolla often needs to be thinned out regularly. This prevents it from completely covering the water’s surface.
• Removal: You can easily remove excess plants with a net to keep its growth in check.

Submerged Water Ferns (Aquarium Plants)

Ferns like Java fern (Microsorum pteropus) and African water fern (Bolbitis heudelotii) are popular choices for aquariums and are cared for differently than floating ferns.

1. Placement:

• Attach to hardscape. These ferns grow from a rhizome, which should not be buried in the substrate. Instead, attach them to rocks, driftwood, or other decorations using fishing line, super glue gel, or thread. Over time, the fern will attach itself.
• Floating is also an option. These ferns can also be left to float freely in the water.

2. Lighting:

• Low to medium light. Most aquarium ferns are low-light plants and can be easily burned by high light. They do not require a special spectrum but will appreciate a standard aquarium light.
• Avoid high light. Too much light can lead to melting or burning of the leaves.

3. Water Conditions:

• pH and temperature: Most aquatic ferns prefer a pH range of 6.0 to 7.5 and temperatures between 68-82°F (20-28°C).
• Nutrient absorption: They absorb nutrients directly from the water column. While not strictly necessary in a tank with fish waste providing nutrients, a liquid fertilizer can help promote healthy growth.
• Slow-growing: These ferns are generally slow-growing, so over-fertilizing can lead to unwanted algae growth.

4. Propagation:

• Plantlets: These ferns will often produce tiny plantlets on their leaves. You can gently remove these and re-attach them elsewhere in the tank to propagate new plants.
• Rhizome division: You can also divide the rhizome with a sharp, clean blade to create new plants.

Important Note on Invasive Species

Some water ferns, particularly Azolla, can be considered invasive in certain regions. They can form dense mats that outcompete native plants, block sunlight, and deoxygenate the water, harming fish and other aquatic life. Check local regulations before introducing any water fern to an outdoor pond or waterway.