Java fern (Microsorum pteropus) is a popular plant in the aquarium hobby, valued for its hardiness and versatility. While it is primarily known for thriving fully submerged, it is naturally an amphibious species. This means it can adapt to both fully aquatic and semi-aquatic environments. The ability of Java fern to grow with its foliage out of the water, known as emersed growth, is often utilized by commercial nurseries to cultivate robust specimens. Successfully cultivating the plant in this state requires specific environmental controls to mimic its natural habitat along the edges of Asian water bodies.
Biological Requirements for Emersed Culture
The primary environmental factor governing the Java fern’s survival out of water is extremely high humidity. When the leaves are exposed to air, they lack the protective water barrier they enjoy when submerged, making them highly susceptible to desiccation. Humidity levels should be maintained close to 80% to 100% to prevent the leaves from drying out.
This high atmospheric moisture reduces the rate of transpiration, the process where plants lose water vapor. The plant’s rhizome, the thick, horizontal stem, must remain consistently moist or partially submerged. If the rhizome is allowed to dry out, the plant will not survive.
A consistent temperature between 72 and 82 degrees Fahrenheit (22 and 28 degrees Celsius) is ideal for emersed growth. The plant gains unlimited access to atmospheric CO2, often leading to more vigorous growth than seen underwater. Providing a steady source of nutrients, through a moist substrate or liquid fertilizer, supports this accelerated growth.
Visual Differences in Emersed Foliage
When Java fern transitions from submerged to emersed growth, the foliage undergoes noticeable morphological changes to adapt to the terrestrial environment. The leaves produced in the air become significantly thicker and more rigid than their delicate aquatic counterparts. This change in leaf structure provides better support and helps the plant retain moisture.
The color of the leaves may deepen to a darker, richer green once fully acclimated. Emersed leaves can also be smaller and have a more textured or leathery feel, which aids in resilience outside of water. The rhizome may also appear tougher and more robust as it adapts to anchoring the plant.
The leaves originally grown underwater will often melt or die back during the transition period. This is a normal part of the process as the plant sheds its aquatic-adapted leaves and produces new foliage specifically suited for the air.
Transitioning and Maintaining a Semi-Aquatic Setup
Moving Java fern from a submerged tank to an emersed setup requires slow acclimation to prevent shock and leaf die-off. A gradual transition, such as placing the plant in a closed container like a paludarium with extremely high humidity, is the recommended method. This allows the plant time to adjust its physiology before being exposed to lower ambient humidity.
When setting up the environment, the Java fern should be anchored to hardscape like driftwood or rock, rather than planting the rhizome directly into the substrate. The rhizome must never be buried, as this will cause it to rot. The roots can be secured with aquarium-safe super glue gel or cotton thread until the plant naturally anchors itself.
Suitable environments for emersed growth include paludariums, terrariums with a water feature, or waterfall walls, all of which naturally maintain the necessary high moisture levels. Maintenance involves frequent misting or a dedicated misting system to ensure the leaves and rhizome remain saturated.
Ensuring adequate airflow is equally important to prevent stagnant air conditions. Poor air circulation can encourage the growth of mold or fungal diseases on the damp leaves, which can quickly harm the plant.