Azolla filiculoides

Cultivation Details

Azolla filiculoides is is mainly found in frost-free climates in the wild and is not frost tolerant. In areas where it does experience frosts, it survives the colder weather by way of overwintering bodies that sink to the bottom in the autumn and rise to the surface in spring only after temperatures have warmed up. This phenomenon does not occur in all areas, nor is it effective if the winters are very cold. In such circumstances it is recommended that some plants be lifted each year in the autumn before the first frosts and overwintered in a saucer of moist soil in a bright frost-free area or in an aquarium - re-introducing them to the pond in the spring^{[1, 2]}. Although of tropical origin, the plant is thought to have evolved a cold-tolerant strain since its introduction into Britain and South Africa, Some forms of the plant may be able to survive temperatures as low as -10°c before death occurs^[3]. Requires a sunny or lightly shaded position in still or slowly flowing water. The plant is able to undergo rapid vegetative reproduction throughout the year by the elongation and fragmentation of the small fronds, and under ideal conditions, the daily rate of increase can exceed 15% with the doubling time being every 4 - 5 days^[3]. If growing this plant, it is very important to ensure that you do not spread it from your pond into the surrounding environment. The most simple way of ensuring this, when removing excess growth from the pond, is to put it into a black plastic bag, seal it and leave it for some weeks to make sure it is completely dead. The resulting material is then an excellent addition to the compost heap^[PFAF]. Plants seldom reproduce by spores^[1]. The genus Azolla is unique in that it has a symbiotic relationship with a blue-green alga, (Anabaena azollae Strasburger), which is located in cavities in the dorsal leaf-lobes. This symbiotic association, which enables the plant to fix atmospheric nitrogen, is the only one known between a fern and a cyanobacterium^{[1, 3]}.