This summer I have introduced the water fern to Under tallarna (Under the pines), a progressive culture and cultivation community in Järna outside of Stockholm.

[Azolla Cultivation and Harvesting at Under tallarna 2015.]

Azolla grows year around in tropical and temperate regions. It’s one of the world’s fastest growing plants and it can be very invasive, in many places it’s considered a weed. In Sweden it can’t survive the winters when the water freezes [Update: It turns out that Azolla actually can survive quite harsh winters with prolonged freezing of the pond water], which is good because it prevents it from spreading uncontrollably. However, in the summer it can grow really well. At Under tallarna we planted a couple of handfulls in July and it covered the whole pond in the photos above, as well as two smaller ponds, in about a month. From then on it has kept growing. In September Under tallarna harvested most of it to try it out as mulch and compost. It’s difficult to know how much nitrogen Azolla fixates from the air, since it also can take up nitrogen from the water, but it should provide both a positive nitrogen and carbon input to the site.

The ducks at Under tallarna eat Azolla, but they also have access to other food and we have not made any effort to measure how much Azolla they eat. We also haven’t tried to determine if the Azolla influences their health or egg production. It might have a positive effect, since it has shown to increase cow’s milk production. On the other hand there are some health concerns with Azolla that I have written about in a previous post. My impression is that the ducks are slightly bothered about the Azolla when it covers the whole surface of their pond, since it makes it more difficult for them to swim and dive, but that they enjoy having it around otherwise.