Marimo moss balls, whose name means “seaweed ball” in Japanese, are a truly unique aquatic plant. They grow in freshwater and are native to just a few lakes in a handful of countries around the world, including in Ireland, Scotland, Japan, Estonia, and Iceland.
Bright green, soft, and perfectly round, marimos are not actually moss at all, but are rather a spherical algal growth known as Aegagropila linnaei.
Moss balls only grow around 5 mm per year, but they can survive for over a hundred years and are often passed down through generations as a family heirloom.
Table of Contents
How to care for a marimo moss ball
Marimo moss balls should be grown in a glass container filled with filtered or distilled water. The water should be changed every two weeks. Marimos require indirect light and need to be kept cool. Their container should be cleaned regularly.
Basic care guidelines for marimo moss balls
Keeping a marimo moss ball is a great alternative to growing regular moss indoors. While they have a similar look, marimo moss balls are grown in water, which means they bring less damp moisture into your home than normal moss does.
Marimo moss balls are happiest living in glass containers full of filtered or distilled water. The better the quality of the water is, the happier your moss ball will be.
The water in their container should be changed every two weeks.
If any algae stains begin to build up around the water line or at the top of the glass container, wash the container out before refilling it.
When washing the container, do not use any cleaning fluid. Instead, use a clean brush or sponge to scrub off any stains and then rinse your container thoroughly with water.
Always make sure that you are using cool or cold water when refilling your container.
You can cover the ground of your container with smooth stones or decorative gravel to beautify it. Moss balls make a great freshwater aquarium plant, so you can use them as a decorative addition to a fish tank.
In fact, it may even be beneficial to do so, because marimos filter nitrates and other toxins out of the water and will act as cleaners for your fish tank.
Marimo moss balls are also an easygoing aquarium plant, as they do not require you to go through the usual normal complicated procedures involved in trimming an aquarium plant or anchoring an aquarium plant.
That said, some fish like marimos a little too much and may begin to eat them. Look into whether your breed of fish likes to eat marimos before you put them in a tank together.
Marimo moss balls grow at the bottom of lakes, and so are not at all partial to direct sunlight. Ideally, they should be getting medium, indirect light.
Keeping them in a room with east-facing windows is best.
Bear in mind that the glass container you are keeping your marimo moss balls in will magnify the sunlight and create a “greenhouse effect,” heating up the water your balls are in.
Marimos are native to cool lakes, and warm water will not agree with them. It may even cause them to turn brown.
Keep your glass container well away from south or west-facing windows, and ideally, at least a meter away from any windows in the room you are keeping it in.
For an explanation of what medium, indirect light is, read this essential guide to light levels for plants.
How to keep your marimo moss balls round
The reason marimo moss balls develop and keep their perfectly spherical shape is explained by the conditions in their native habitat.
Marimo moss balls live on the floor of freshwater lakes, where they are pushed and pulled along by natural currents and waves.
This movement across the hard ground causes marimos to roll around and facilitates equal exposure to all conditions across the surface of the whole ball. This causes them to grow evenly.
Because your glass, water-filled container will not have currents or waves, you will need to mimic their effects!
Make sure your balls are not just sitting on one side for months, as their growth will become uneven as a result. Instead, move your container around so that the moss balls roll around too.
If your container is too heavy to move, use a large spoon to move the water around so that your moss balls are carried along the ground and repositioned elsewhere in the container.
Problems with marimo moss balls
The most common problem marimo moss balls have is that that they begin to turn brown when they are not happy with their environment.
This usually happens when they are exposed to light that is too bright or are kept in water that is too warm.
The problem is easily solved by moving your container to an area in your home with lower light levels.
If you notice that the water you are growing your moss balls has become too warm because of the sunlight or the temperature of the day, change it out for cooler water immediately.
Another problem that has recently emerged, is that zebra mussels have been found in imported Marimo moss balls in the United States.
Zebra mussels are an invasive species. If you find any in your moss balls, read and follow the U.S. Fish and Wildlife Service’s guidelines on how to dispose of zebra mussels.
Frequently asked questions about marimo moss balls
Why are my marimo moss balls floating?
Marimos will float if air has become trapped inside them. You can squeeze them gently to get out any trapped air. Marimos often float when they are placed inside a new container and then sink down to the bottom after several days.
Can a marimo moss ball survive outside of water?
While marimos can be kept out of water for a few days, they cannot live outside of water. To keep them alive while out of the water, place them in a sealed container or plastic bag with a little bit of water. Check on them regularly to make sure they are not drying out.
Daniel has been a plant enthusiast for over 20 years. He owns hundreds of houseplants and prepares for the chili growing seasons yearly with great anticipation. His favorite plants are plant species in the Araceae family, such as Monstera, Philodendron, and Anthurium. He also loves gardening and is growing hot peppers, tomatoes, and many more vegetables.