marimo "moss" balls

marimo "moss" balls

Posted by Megan Nichols on Dec 21st 2019

Marimo Balls are one of the more intriguing plants we’ve come across in the last year. Though not expensive or in as high demand as some, these crazy, fuzzy, aquatic green balls have captured our hearts. No surprise there, given the story of their origin.

It is said that Marimo originated from two young people in Japan who were forbidden to be together, so they  ran away and plunged into a lake. Once joined together forever they became Marimo. Now when given as a gift, Marimo is considered a token of everlasting love and is said to manifest the desires of the heart for the giver and reciever. Romeo and Juliet didn’t even leave that legacy.

This amazing plant, though often referred to as a moss ball, is not made of moss at all. In Japanese “mari” translates to ball and “mo” translates to algae or seaweed. Given the sometimes-negative view of algae, however, they are affectionately known as “moss balls.” Whatever you call them, these beautiful spheres are as easy to care for as they are intriguing to behold, and they make a great addition to every plant-lovers collection.


Marimo like bright, indirect light. Direct sunlight is not recommended unless it is for a very short time and is low intensity (such as morning light). Sunlight increases the temperature of water in glass and can make the Marimo sick.


Marimo grow naturally in freshwater. When domesticated, it’s best to keep them in distilled or rainwater. If using tap water, let it sit in an open pitcher for at least 24 hours. Change the water in your Marimo’s tank or vessel every one to two weeks. If added to an aquarium, remove the balls every week, give them a gentle squeeze and rinse, then let them sit in water in the fridge for a few hours before returning them to the tank.


Lakes are naturally cool, so Marimo prefer to stay on the cooler side.  


Marimo make their own food (like all plants) through photosynthesis. It is OK to fertilize your Marimo if you’d like as this may make it grow more quickly. Specific Marimo food can be purchased at aquatic pet stores or on Amazon.  

For the love of plants

  • Marimo can live for over 100 years.
  • Marimo are extremely slow growing, but have been found as large as 12 inches in diameter in their natural habitat. Most of the known population resides in two freshwater lakes in Japan and Iceland.
  • In their natural habitat, Marimo bounce and roll along the bottom of the lake. Without the natural water current they can become flat on one side. Roll Marimo in your hands to keep them round and to avoid or correct flat spots.
  • Marimo balls will float and sink based on their response to daylight and their own internal clock. Marimo’s numbers in the wild have declined significantly, and they are a legally protected species where they naturally occur. Scientists are studying the benefits to the Marimo of floating and sinking in hopes they might learn why they are declining in number and how to help increase the population.
  • Grow them on their own or as part of collection. They make a fun addition to freshwater tanks. Beta fish may even roll them along the floor of the tank, doing some of the work of keeping them round for you.