I saw some moss balls for sale in the gift shop of the new Nordic Museum. What type of moss is used? Is it native to Nordic countries? How do I care for one indoors?
The “moss” is actually a type of freshwater alga, Aegagropila linnaei, found in only a small number of northern hemisphere lakes. Other common names are lake ball or Cladophora ball. In Japan, they are called marimo (meaning a bouncy ball that is in water). The Ainu people of Hokkaido hold an annual Marimo Festival at Lake Akan to celebrate these charming lake goblins.
Iceland’s Lake Mývatn once had the world’s largest colony of lake balls but pollution has been altering the ecosystem there, and the mats of algae balls (colloquially called round sh*t or muck balls by the fishing community) began dying out. Their disappearance was first noted in 2013. There are some recent signs that the nutrient imbalance of the lake (caused by fertilizer runoff, and accumulation of bacteria) is correcting itself and that the ecosystem of the lake is bouncing back to better health.
To grow marimo inside, you will need a container that holds water, and a spot where the algae receive indirect sunlight. They prefer cool locations in nature, so they will do best if they do not get too hot (don’t put them near a heat source, and if it gets hot in your home, you can cool them off in water in the refrigerator). To keep the balls floating, squeeze out some of the water from time to time. To propagate the algae, use scissors to divide the marimo in half after squeezing out some of the water (you can repeat this process and cut into fourths or eighths). Use thread to wrap the cut algae back into a rounded shape, tie the thread close to the ball, and put back into the water. Some people combine them with other plants and tiny shrimp in indoor aquascapes.