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How to Propagate Marimo (Freshwater Algae)

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Large (left) and small (right) marimo balls

Large (left) and small (right) marimo balls

Marimo Propagation

Marimo (Cladophora aegagropila) is a variety of freshwater algae that is common in the northern hemisphere. The spherical shape occurs in nature by water currents that cause the marimo to tumble on lake beds. The tumbling retains the spherical shape of marimo.

"Marimo" is a Japanese word that literally means “ball seaweed.” It is native to Japan, Iceland, Scotland, and Estonia and has been a protected species in Japan since as early as 1920. An annual three-day marimo festival is held in Japan to pay tribute to this algae. It is also classified as a protected species in Iceland.

Marimo can be grown indoors and propagated to create smaller marimo. Propagation is very easy and rewarding.

Dividing the algae is the best method of propagation. Retaining the spherical shape is accomplished differently compared to nature's process of tumbling marimo on the bottom of lake beds. Thread is used to tie the division into a ball to ensure a spherical shape as it grows.

Materials Needed

  • Marimo
  • Scissors
  • Thread
  • Container (jar, glass, fish tank, etc)
  • Water
A small division removed from a parent marimo.

A small division removed from a parent marimo.

How to Divide Marimo

Dividing marimo is simple to accomplish. The picture above shows one that is about an inch and a half wide, which is large enough to perform a division.

  1. Select marimo of a decent size to be divided.
  2. Decide how to divide it (halves, thirds, quarters, etc).
  3. Gently squeeze the marimo to drain excess water. This makes it easier to cut with scissors.
  4. Use a sharp pair of scissors to cut it into desired divisions. Marimo consists of many small filaments of algae bundled together, so cutting them apart will not harm the overall health of the ball.
  5. Form the fresh divisions into a ball by rolling between the hands.
  6. Use a piece of thread to wrap around the new divisions and tie the ends together. This will retain the spherical shape.
  7. Place the new divisions into a container full of water. Do not use distilled water, because it lacks vital minerals. Marimo needs minerals that are available in tap water. Chlorine-free tap water is preferred. Leave a container of tap water to sit overnight to allow the chlorine to dissipate.

Marimo grows very slowly (around 5mm per year), so do not worry if the divisions appear to lie dormant. The tiny filaments of algae will eventually grow thick enough to cover the thread used to retain the spherical shape.

How to Care for This Algae

Water Requirements

Marimo is very easy to care for. It does not need aeration or filtration, but the water must be changed regularly to keep it healthy. Water changes should occur weekly. Rinse the marimo with water to remove debris and buildup. When rinsing, give it a gentle squeeze, like wringing out a sponge. This helps remove buildup and debris as well.

Light Requirements

Marimo has adapted to low-light conditions due to their native residence on the bottom of lakes. Too much sunlight will cause discoloration, so placing in indirect sunlight is ideal.

Artificial lighting, such as household light bulbs, is sufficient and will greatly reduce the chance of burning caused by strong sunlight.

Growing Marimo in a Fish Tank

Growing marimo in a fish tank may cause a few minor problems to arise. Tanks with pump filters can become clogged around the intake and filter due to filaments being sucked into the filter. The buildup will reduce the effectiveness of the filter, and the filter and pump will require cleaning.

Marimo may also be a target for some fish. Goldfish and bottom dwellers that scavenge will nip and slowly pick it apart. This will also increase the number of filaments being sucked into the filter, as well as reduce the size of this algae. The loose filaments can also add to algae growth in the tank. The glass and tank may need to be cleaned more regularly if algae begin to flourish.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.


cindy magbee on August 28, 2018:

I found something in the woods in a bottle in alabama. Is it possible its a marimo it sure looks like one. If not does anyone know what it is

Deborah Minter from U.S, California on April 14, 2018:

Good article! The marimo ball has always been one of my favorite aquatic plants.

Angel on July 07, 2014:

You can buy the moss balls AKA round Marimo algae on eBay at a very reasonable price I purchased one 2 years ago and mine is very Large now I am purchasing 6 more on eBay today I love mine very unique item.

Sean Hemmer (author) from Wisconsin, USA on September 08, 2012:

renee rompies - That is amazing. Must have taken many years to reach that size. I have a misshapen marimo that is starting to flatten and I'm thinking about doing the same.

renee rompies on September 08, 2012:

I have our two the size of grapefruits also put some on rock and it grew a across like a carpet

Sean Hemmer (author) from Wisconsin, USA on August 26, 2012:

theraggededge - Haha, I have no idea. Its similar to seaweed, so maybe? I think the texture would be really off...kind of like chewing a wet cotton ball.

Bev G from Wales, UK on June 16, 2012:

Never heard of it. Looks really interesting. Is it edible (not that I want to eat it!)?

Sean Hemmer (author) from Wisconsin, USA on June 11, 2012:

Janis - I found out about marimo while searching for aquarium plants. I decided to buy 3 marimo balls and I'm glad I did. I have 6 now via divisions, but the newly divided ones are still pretty small.

c1234rystal - Marimo algae itself is common to the northern hemisphere, but the conditions to produce marimo balls are unique to a few countries. Water currents play a vital role in causing the algae to bundle together.

GoodLady - You may be able to find marimo in pet shops over there. I had to order online, since all the shops in my area had no idea what I was talking about. Marimo ships well due to their low requirements. As long as they are moist, they will survive. Avoid "nano marimo" though. They are very small and not worth the price.

Johnathan L Groom from Bristol, CT on June 11, 2012:

detailed and catagorized work here...

Penelope Hart from Rome, Italy on June 10, 2012:

I want one marimo - it is the most interesting Hub. I think marimo would make my 2 year old happy in her room, but where could I find it in Italy?

c1234rystal on June 10, 2012:

Interesting hub; just one question. How is Marimo native to places as far from each other as Japan and Estonia? It must have migrated from one place to the other. Do you know where exactly it originated? :)

Janis Goad on June 10, 2012:

Interesting hub, SEH110. I never heard of Marimo before. How did you run across them?