How to Care for Marimo Moss Balls—Plus Why They Are So Hard to Find Right Now

This once-trendy plant is off the market (at least for now).

Marimo moss ball in water
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Marimo, more commonly known as moss balls, make a fun addition to your indoor garden and are a popular feature in aquariums. These aquatic plants are also relatively easy to care for once you know the basics. Because they're low-maintenance and add interest to a plant collection, marimo moss balls were on-trend, until they were found in 2021 to harbor invasive zebra mussels. For now, moss ball sales are on pause in the U.S., but here are the marimo moss ball care tips to follow once they return, according to Lisa Eldred Steinkopf, founder of the Houseplant Guru and author of Houseplant Party.

What Is a Marimo Moss Ball?

The botanical name for marimo moss balls is Aegagropila linnaei. The common name, marimo, is Japanese for "seaweed balls." The little green spheres are not actually moss, but algae. In their natural habitat, the algae balls live at the bottom of cold lakes. They keep their round shape by the action of the waves. "They naturally grow in cool lakes in Japan and Iceland and are a protected species because they are endangered in their natural habitat," explains Steinkopf. For this reason, once you can buy moss balls again, you'll want to look for those that are domestically cultivated using environmentally friendly methods at select plant stores and aquarium supply shops.

Are Marimo Moss Balls Safe Again?

Starting in winter 2021, the sale of marimo moss balls suddenly slowed when zebra mussels, an invasive species that disrupts the food chain, were found hiding in imported marimo moss balls throughout the U.S., according to the U.S. Fish and Wildlife Service. If you bought a moss ball after February 1, 2021, it's recommended that it be properly destroyed in order to prevent zebra mussels from getting into local waterways. For now, we'll have to wait to introduce these plants into our homes. But once it's safe to do so again, these marimo moss ball care tips will keep your long-awaited aquatic plants happy and healthy.

How to Care for Marimo Moss Balls

Marimo moss balls are not hard to care for and make an excellent plant for first-time plant parents. However, to ensure your moss balls thrive, here are some care tips.


The good news is, marimo balls do not need a lot of light to thrive. "They don't need to be in bright sun since they naturally grow at the bottom of the lakes," says Steinkopf. "They prefer a lower light situation." The algae do not like direct sun and should not be placed near a window, as marimo can quickly turn brown if they are getting too much direct light. Keeping them out of direct sunlight and giving them plenty of low, indirect light should keep them happy.


Moss balls are aquatic plants, so they must live submerged in cool water, preferably under 77 degrees Fahrenheit. These plants aren't too picky about the type of water; it just has to be freshwater. "I use my tap water, but well water, distilled water, or rainwater would be fine as well," says Steinkopf. For best results, change the water every two weeks and allow the water to sit out for a day beforehand, so chlorine has a chance to evaporate. Also, clean the container with a brush if algae start to grow on the surface.


Marimo does not require supplemental fertilizer! These amazing plants make their food through photosynthesis and do not need a nutrient boost to keep them thriving. They are slow-growing, so don't expect them to outgrow their tanks within a year. The plants grow up to 5 millimeters per year and will eventually reach 2 to 5 inches in containers or 8 to 12 inches in natural conditions.

Common Problems With Marimo Moss Balls

Besides turning brown from too much or insufficient light, some marimo moss balls will occasionally float or lose their round shape. Floating occurs due to trapped air bubbles in the plant. To get them to sink again, give them a gentle squeeze to pop the air bubble. The marimo will sink to the bottom of the tank within a couple of days. Marimo can lose their round shape due to a lack of agitation in the water. Remember, it's the wave motion that keeps them round in their natural habitat. "They need to be swirled around in the bowl they are in to mimic that environment and keep them round," says Steinkopf. "It also helps them get light around the ball. If one side doesn't ever get any light, it will turn brown."

How to Propagate Moss Balls

Marimo balls are easy to propagate. "Pieces of them can be pulled off to make new ones," says Steinkopf. Cut the ball in half and shape it into a ball. You may need to use twine to hold the shape of the ball until it's established. Place it in the bowl of water, and turn it at least once a week to encourage growth all around.

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