The Legend of the Marimo Moss Ball
- Savannah Scollar
- Mar 11
- 4 min read
Updated: Mar 12
This article was originally published in Washington Gardener Magazine.
Marimo moss balls move and groove in ways that few other plants could even dream of! During photosynthesis, these adorable aquatic spheres produce little air bubbles, which lift them up, closer to the water's surface. Though "pet" marimo moss balls tend to be about an inch or two wide, the wild ones are much larger.
Lake Akan, in Hokkaido, Japan, is the primary home of these wild marimo moss balls. The name "marimo" is Japanese, with "mari" meaning ball and "mo" meaning aquatic plant. Some of the moss balls in this lake are 12 inches wide. It's amazing, especially when you consider that these things only grow, at most, half an inch per year.
The marimo "moss" balls are actually made from a rare species of branching filamentous algae, native to Japan, but also present in Europe and parts of North America. In most of its habitats, the algae grows as floating mats, or as fluffy green wigs for underwater rocks. Lake Akan, however, is one of the few locations where conditions are right for the magical formation of the marimo balls. The wind moves the moss balls in the lake, spinning them over and over and keeping them in shape. The smallest marimo sleep at the bottom of the lake, while the larger ones rest at the top of their underwater pile.
As with many of nature's most amazing creations, the wild marimo balls have faced their fair share of threats. In 1898, as soon as the marimo balls were given their name, they were put in danger. People loved them too much- taking them, buying them, and selling them faster than they could grow. In 1920, the marimo balls were named as a Japanese Natural Treasure. This, unfortunately, resulted in even more of the moss balls being taken from lakes. Pollution only served to worsen the plight of the marimo.
In October of 1950, people decided to stand up against the damage being done. They gathered to return many of the marimo balls to Lake Akan. This was the origin of the Marimo Festival. Every October, since 1950, Hokkaido's indigenous Ainu people have held a festival celebrating the marimo moss of Lake Akan, with song, dance, and ceremonies. This helped to encourage conservation and save the marimo from threats of extinction.
The appreciation of the moss balls is far from an ancient tradition. Originally, many indigenous people viewed the marimo balls as something annoying that got tangled in fishing nets. After people started coming to the lake and taking the marimo moss away, the Ainu people decided that the marimo needed their help. Marimo moss, like other plants, is an important part of the ecosystem, keeping everything balanced. Without the marimo festival, who knows if we'd even still have these moss balls?
In certain European lakes where conditions had once been right for the moss balls to form, pollution and other issues led to their downfall- reducing their populations or eliminating them entirely. Now, only a few of these European lakes have marimo balls: Lake Myvatn in Iceland and the Shatsk lakes in Ukraine.
Semi-recently, the marimo balls were wrapped up in yet another scandal. Around 2021, invasive mollusks were being found in moss balls sold in stores. Because of this, even to this day, you might have trouble searching for marimo to buy in person.
Zebra mollusks are probably some of the all time worst invasive species. They breed ridiculously fast, clog pipes, ruin beaches, obliterate water quality, and outcompete local wildlife. The government spends 500 million dollars each year, combating zebra mollusks in the great lakes.
It's unclear whether this problem with marimo has been resolved. People discuss "bans" and marimo being "illegal", but I was unable to find any information regarding official restrictions. Since the zebra mollusks are European in origin, it might be best to buy tank-grown marimo from the US or Asia.
Moss balls, over time, can fall apart and turn into smaller moss balls. Each moss ball exists as a colony of organisms rather than a singular plant, so you don't have to worry too much about hurting them. Moss balls can be rolled by hand, or shaped with felting needles. At Easy Little Plants, I use the felting needle strategy to turn marimo tufts into tiny moss balls, the size of a pea. I like making kits with these tiny moss balls, so people can enjoy them as an activity. It's fun and relaxing to decorate the jars and set everything up. If you're interested, you can pick up a cute kit from my shop in Olney! The marimo balls are ridiculously resilient and can go a long time without light or attention. They make great gift plants for this reason. You don't really have to worry about accidentally killing them in the time between buying and gifting.
When it comes to care, the marimo balls are incredibly laidback. They can live in any container of tap water. There's really no need to dechlorinate the water or use rainwater, as they're not that picky. Based on their natural habitats, they seem to like water with a good amount of calcium. Aquarium calcium might serve as a good treat to encourage your marimo to grow, but it's totally optional. Distilled water, which doesn't have any nutrients, would probably be counterproductive, even though it's commonly recommended.
By the way, be careful not to let your marimo sunburn! Marimo balls turn brown in intense sunlight and prefer something more gentle. Save those windowsills for your succulents! The marimo would rather be a few feet away.
I change the water out when it starts to look funky, every month or so. If you have shells or stones decorating the container in which your moss balls reside, a pipette or turkey baster can come in handy. With these special tools, you can remove the funky water without the risk of dumping everything else out.
Marimo also do well in aquariums, especially with cherry shrimp. These tiny and brightly colored crustaceans enjoy standing on top of the moss balls and searching for food. Soon, I'll be moving my betta fish, Olive, to a much bigger tank at my shop. I'll decorate it with plenty of plants of course! The smaller tank? That'll keep on running, with the introduction of its new tennants: cherry shrimp and marimo moss balls!
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