What are Marimo Balls? Why Do People Keep Them?

Way back when (ok, not that long ago though, I’m not that ancient!) when I was attending college and living in a dorm, I sadly couldn’t keep any pets. Plants were allowed though. When are plants ever not allowed? That would be weird. Anyways, plants were allowed and among my newly blossoming plant horde I had an adorable Marimo ball.

When I graduated I ended up passing my Marimo on to a friend. Years later, I tried to buy another Marimo but had trouble finding any for sale. Around early 2021 some Marimo balls imported into the US were found to be infested with devastatingly invasive zebra mussels. US Fish & Wildlife advised anyone who purchased a Marimo ball after February 1st, 2021, to destroy them. The adorable aquatic balls became nearly impossible to find for sale throughout the US, and rightly so. Zebra mussels are highly invasive and can destroy natural ecosystems as well as damage essential underwater infrastructure, such as water delivery pipes.

So why am I writing this if Marimo balls are impossible to find? In recent years Marimo balls have become available to purchase again, mostly through online vendors. US sellers typically cultivate their Marimo within the US, in set ups free from zebra mussels, rather than importing them. I was excited to recently purchase a few little Marimo balls of my own! So what exactly are Marimo balls? Where can you purchase Marimo that are free from invasive zebra mussels? And why would anyone want to keep Marimo balls in the first place?

What, Exactly, Are Marimo Balls!?

It’s a plant, it’s a moss….Well, it’s actually algae! Despite oftentimes being called Marimo moss or Marimo moss balls, true Marimo is a type of algae. It’s Latin name is Aegagropila linnaei. The type of algae that makes up Marimo balls is actually considered to be endangered in the wild! It’s native to cold water lakes notably in Japan and Iceland.

The name Marimo is Japanese and translates to “ball water plant”. Although Marimo balls are most common among keepers, the algae actually comes in three growth forms. It can grow flat on surfaces such as driftwood, rocks, and the bottom of lake beds. It it sometimes used this way as a carpeting plant in aquariums. Marimo can also exist as free-floating filaments within the water column. And, it’s most popular form, it can form densely packed balls. Marimo balls form in nature within lakes. The current of the water constantly moves and rotates the algae which helps it to maintain it’s adorably round shape.

A Japanese National Treasure

In Japan, Marimo balls have been declared a national treasure! They are seen as symbols of love, good luck, and prosperity.

According to Japanese folklore, the beautiful daughter of a chief from a tribe living near lake Akan, fell in love with a commoner. The young lovers were forbidden from seeing each other, so ran away together. While making their escape the couple fell into Lake Akan and sunk down into the depths. They turned into Marimo balls, and thus were able to stay together forever.

The Ainu people in Japan still celebrate Marimo today! Every October they celebrate a 3 day Marimo festival on the banks of Lake Akan. To protect the Marimo, it’s now illegal to collect the algae directly from Lake Akan. But Marimo balls are still commonly given as gifts, sold as souvenirs, and used as living home decor.

Where Can You Buy Marimo Balls?

It’s important to purchase your Marimo from trusted sellers who sell zebra mussel free algae. Recently a few different stores selling Marimo within the US have popped up. I’m hesitant to recommend specific stores without actually trying them out for myself first. I’m planning on purchasing Marimo from a few different sellers, and will update this section accordingly.

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So far, the only seller I’ve personally purchased Marimo from is Lonza Shoes on eBay. I bought 0.25inch Marimo balls from this listing, and for just under $16 received 5 adorable little Marimo. My Marimo got to me in March of 2024, so at the time of writing this I haven’t had them for very long. I’m quarantining them for a bit before decorating their jar more, which is why it looks bare in the photos here. I’ll be sure to come back and update this post after I’ve had my Marimo for longer! I’ll also update and share if I decide to try out any other sellers.

Remember that no matter where you get your Marimo, I personally feel that it’s important to quarantine them! I’m planning on keeping my Marimo in a bare bottom jar for 6 months before adding any additional decor. Quarantine is especially important if you’re planning on adding Marimo to an already established aquarium.

Watch Out For Fake Marimo Balls!

Especially around the time of the zebra mussel fiasco, fake Marimo balls began showing up for sale. Some of these fakes are live plants that are not made up of Aegagropila linnaei. The most common example I’ve seen is java moss balls being sold as Marimo. The main difference is that java moss does not naturally form balls the way that Aegagropila linnaei does, so the java moss balls are commonly tied into a ball shape with fishing line or other types of fine string. It’s unlikely that these plants will remain healthy and continue to grow in the shape of a ball the way that an actual Marimo does.

There are companies that sell Marimo balls with artificial cores. This has become something of a controversy in the Marimo keeping world. These Marimo balls are typically made of up true Aegagropila linnaei, but instead of pure algae they consist of some type of artificial ball in the center surrounded by a thin outer layer of Marimo algae. Personally this was something I preferred to avoid when it came to purchasing Marimo for myself. But it doesn’t bother everyone, and that’s ok too. As long as you are careful and know what you are getting!

Wait, So Why Do People Like Marimo So Much Anyways!?

Some people purchase Marimo balls as cool looking additions to their freshwater aquariums. Freshwater shrimp especially love them!

Personally I think of my Marimo balls as cute, unique houseplants. I keep and enjoy them for similar reasons why anyone would like any other type of plant. I keep my Marimo in a decorative jar in my bedroom. I think they look nice. They add a pop of life and bring a little bit of the natural world into my house. Marimo are low maintenance and easy to care for. With proper care, they can live a really long time (over 100 years!). I purposely purchased small Marimo balls because I think it will be fun to hopefully watch them grow over the years. I enjoy house plants in general, especially unique house plants. You don’t get much more unique than a cute little aquatic algae ball.

There’s just something special about Marimo. I don’t know exactly what it is, but it feels like they have more personality than other house plants. Plant-ality? They almost blur the line between house plant and pet. Because of how they form in nature they are more mobile than your typical potted plant. I try to remember to stir my Marimo daily to simulate lake currents and help them maintain their shape. Sometimes when Marimo photosynthesize little bubbles of oxygen will get trapped inside the algae, and it makes the Marimo temporarily float.

They’re just cool, cute, unique plants! There’s lots of reasons to enjoy Marimo!