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Marimo, Japanese Moss Ball

A year ago I came across a mention of Marimo somewhere on the net. I had forgotten about them until a couple of weeks ago I found myself in an aquarium store and saw some in a fish tank. Since this was a serious kind of aquarium shop they were labeled "Japanese moss balls" but I recognized it right away as a "Marimo." Being one of those suckers born every minute I had to have one if only for the plant geek points. Lately I've been sort of uninspired with collection of indoor plants and have had the strangest urge to grow mosses and ferns. Which is partly responsible for the lack of updates here. I don't know why but lately but plants that are little more than boring green mounds have seemed like something I want to grow.
marimo, Japanese moss ball growing in a jar of water

Anyway, this is my Marimo that I have named Maximus and here he is in a jar of water taking in some morning sun while browsing some garden blogs. Since he doesn't have hands he can't comment but he enjoys reading them. Marimos are actually a fresh water algae (Cladophora aegagropila) and information on them on the internet has to be gleaned from reading from various sources. Fish tank nerds seem to be at the forefront in the U.S.
Domestic Marimo can be grown in tap water at room temperature and be given small amounts of liquid fertilizer with half water changes on a weekly basis. The amount of light it needs varies from source to source. Some places say this plant needs high light while others say it requires little more than ambient light.
Marimo, Japanese moss ball out of water.They're native to Japan and Russia and supposedly Iowa, of all places. They develop their characteristically round shape because water currents push them around the bottom of lake beds. This Marimo is more of an egg shape because it was growing in a colony pressed up against a corner of the plant tank at the aquarium shop I bought it at.
They "reproduce" when a bump forms on a Marimo and it falls off and gets pushed around until it forms the round shape. If you don't want to wait for that you can tear it apart. You can clean your Marimo by dipping it in water and gently squeezing like you would a dirty sponge.
From my lurking at fish tank forums I've gathered that you can find fake Marimos in a lot of places, PETCO being the biggest seller of them. If you buy a Marimo that floats around your fish tank chances are that you've purchased Java Moss wrapped in a ping pong ball.
Maximus looks a little sorry growing in a jar so I may use him as an excuse to purchase a small aquarium to grow him and other aquatic plants and maybe a fish.

Marimo-on Wikipedia.


  1. Hadn't heard of Marimo - must look into this. Several years ago there was a magazine feature (Martha Stewart?) on growing aquatic plants indoors in huge glass vases. I snagged a cheap vase someplace and took a couple of plants out of the aquarium. Eventually I got tired of changing the water to keep it looking good and dismantled the thing. I think I still have that vase...

  2. MBT, the sea is calling to you! That has to be why you have the sudden urge to cultivate moss creatures. I wonder if squeezing them stimulates their reproductive cycle? You could start a new craze like pet rocks with these things. They would be a hit with secretaries, I can tell you. Great for easing the effects of carpal tunnel syndrome and adding a spot of color on the desk. What fun! Better than chia pets.

  3. Go for it! The selfish part of me hopes that this tiny marimo soon will evolve into a full fledge hydroponic system (that way I won't be the only crazy indoor aquaponic gardener around ;) )

  4. How exciting. Or not. Nice color though.

  5. This is actually very cool, Mr. BT!!! I want one now!

  6. Well, this is different! I've never really thought about this subject before. It certainly would make for great conversation when someone asks you what your hobbies are. Very interesting. Hope you have some more info in the future.

  7. Anonymous2:17 PM

    That is cool stuff...I love moss and lichens of all sorts. I love the intense green color it has.

  8. Be careful. I've seen it all too often, you start with a little 10 gallon aquarium and before you know what hit your wallet there's a 150 gallon tank sitting in the living room. (but there's nothing quite like a freshwater 'garden') to keep you busy year round)

    speaking from experience

  9. Anonymous2:32 PM

    Hi! I purchased five marimos on ebay from the UK 12 days ago and I received them here yesterday. I actually got 6, seller put in a small extra for me. They were shipped in an envelope so you can imagine after 11 days of no water and sunlight some of them had small brown patches. The ones that are brown are currently in their own vase with a direct lamp hovering overhead and the others are in my 5 gallon betta tank. I think marimo are so cute and I just wanted to comment on your blog.


  10. Now this is pretty darn cool--because it is strange. I mean, could you iamgine people in offices having jars of moss balls (hmmm) instead of half dead things?

  11. This is almost as amazing as my lucky bamboo plant. I bought a small stalk of lucky bamboo from a tent sale kind-of-thing around August and now it's around 2 feet tall. It's amazing what plants can do with only water.

  12. Anonymous5:33 PM

    Always fascinating info, Mr. Brown Thumb. I never know what you'll next discover. Cute little guy, Maximus is.~~Dee

  13. I think Maximus is a doll! I want to try one as well, but I don't think I could put one in the tank with my water garden goldfish. They grew very accustomed to eating algae and whatever else they could find while outdoors, and now they're eating the aquatic plants I have in the tank with them! (And I feed them every day...guess they miss the mosquito larvae from last summer.)

  14. That stuff is way cool! I'm going to PETCO pronto.

  15. Wishing you contentment, peace, joy and fulfillment during this upcoming year of 2009! (In other words, Happy New Year!) ;-)

  16. This is actually very cool...and weird. I see the attraction and yes, you should go buy a small aquarium!

  17. Anonymous5:05 AM

    Marimos have more personality than a pet rock. I want one!

    Do you think you could make one reproduce with a fish airstone and pump?

  18. Anonymous9:20 AM

    Hi...I am a Mariomo fan. To the person who got them on eBay and they turned brown: Marimo like low, indirect light. The brown spots should resolve, but if not...put a little salt in the bowl. Don't change your water too often (once a week should be enough). I have heard that if you over-light them they will go brown. I have several (15?) Marimo of different sizes, and I give them as hostess gifts when we have dinner with friends. Marimo can be purchased on eBay. the plants at Petco have dubious reputations. There are also sites that sell aquarium plants which sell the Marimo.

  19. Anonymous1:25 AM

    i have a marimo ball in my aquarium. i've had it for about 5 months, and i'm still entirely enchanted by it. i have red cherry shrimp that love it. it moves around the tank and earlier today i found a separate little piece from it, i'm hoping for babies :)

  20. I don't know what happened to my reply comment but thanks everyone for stopping by and commenting.

    Red, I know you can tear off a piece and grow a new one.

    Anonymous thanks for providing info.

    Anonymous, I want some of those little shrimp too.

  21. pearlheartgtr1:27 AM

    I have round about 100 of them in my 55 gallon unheated and planted tank. I started with 3 and couldn't get enough of them!

    As a matter of fact, I have 50+ more coming from my supplier in the UK.

    I have several species of shrimp (about 70 and more are coming) and lots of fish. The shrimp hid all the time until I filled the tank with marimos.

    I do a 50% water change weekly (because of the fish load). I had a bad algae problem before I got the marimos and after I had about a dozen in the tank, the algae problem disappeared. Those little buggers eat up the excess nutrients like it's going out of style.

    I plan on setting up some cultivation bins with the new stock I am getting to sell.

    My sister says I have a problem worthy of an intervention (she keeps coming home to green tribble explosions in my tank). But I tell her I could have worse addictions.

  22. Hi, as people have mentioned above, the perfect thing to have with a mossball is not fish, but freshwater shrimp! Especially if you want to avoid 'tank creep' and stay small.. You can keep Maximus with a few hardy shrimp in something as small as 10L (2 gallon). In fact that is what I am doing.. the modern nano-cubes are good for this and most come complete except for shrimp.

    Has Maximus 'pearled' yet? that is always fantastic, he should rise to the surface on his own then for a day or to.

  23. @pearlheartgtr,

    Your collection sounds awesome thanks for the tips.


    Thanks for sharing your pic of your nano tank.

    Maximus has pearled and I've noticed the rising when the shades are drawn and how he sinks when it is bright.

  24. Anonymous7:06 AM

    if you had the marimo in a tank with a fish and other plants such as frogs bit the fish and sun light wwould be all the foood it needed i have 5 and one my fish actualy move them around for me its ltke a giant bean bag chair for them . the fish even tucked one into the rock cave as im sure asoft pillow someprotection and decoration.. must get afish tank aquatic plants are awesome just dont use ay kindof plant food because the fish waste is enough and man made plant food tends to be to strong for most aquatic plants just clean water natural sunlight by awindow aplant bulb for winter and night andthe fishy waste

  25. Anonymous12:44 PM

    Thanks for sharing your pic of your nano tank.

  26. hey all thanks for the valuable comments. i just got my marimo like 2 weeks ago and realised that there're brown patches on it!!! is it sick? what should i do??
    and 2) i heard that marimo feed on algae, is it good if i add in some of my aquarium water into marimo bottle onve every week? so that marimo have something to feed on.
    and and 3) the idea of putting the cherry shrimp in together with marimo really sound nice. But my marimo is now staying in a 2L capped bottle. is it possible to just add in one shrimp? will presence them both be enough to provide nutrients, food and oxygen for each other?

  27. @Anonymous, You're welcomed. Sorry for the late reply.

    @Lynn, The brown patches could be a sign that there's something wrong with it, or there was something wrong with it. I haven't heard that they feed on algae, they are an algae themselves so that would be kind of weird for them to feed on themselves. I don't know about the shrimp, since I never bought any for it. If you're growing in something so small it probably isn't such a good place for a live "animal."

  28. Anonymous6:33 PM

    Not all PETCOs sell fakes. After watching an anime that had a Marimo in it, I went to PETCO today and bought their last one. It must have been there for awhile because the sales associate had to hunt down the price on a computer. No ping pong ball, sinks like a rock (no rock, either ^^) not quite round as it was squashed in the corner of an aquarium. I have it in a large-mouth Ball canning jar on top of the TV. It's about 2" in diameter x 1.5" thick. I like it!

  29. OMFG I <3 Marimo! All I have is a teens one from a cellphone charm, but I really want more! :3
    I'm temepted to get a little aquarium now!


    But the little glass jar it came in on my cellphone strap ended up cracking, which made me super sad, so I need to hunt down a little plastic jar about the same size. xD

  30. Anonymous11:44 PM

    I just bought a Moss Ball and named him Henry. As I was researching about them I came across this site and was greatly excited to see others have them too and name them even! I originally bought this as a joke, but now I love it!! Thanks for all the info about them too!!

  31. Anonymous9:51 AM

    Just purchased a Marimo at PetSmart--named it Mario. I have 6 ghost shrimp in the aquarium who love to nibble on it...then they turn green inside!!!

  32. Anonymous3:50 PM

    i have 3 small ones i bought from japan a couple of years ago, as i heard once big enough they are worth quite a lot over there! i also thought they looked a bit cute in their mini portable tanks and was amused by it all, reading this it's made me more attached to my moss balls and i would love to give them names if i could remember which is which!

  33. One piece8:08 AM

    Thats zoro =D

  34. Anonymous2:59 AM

    Can anyone help me? My new marimo seem to have bald spots (lighter spots that are less fuzzy) and little round white things are stuck to them, I'm afraid they could be bug eggs?

  35. Anonymous11:29 AM

    a little bit of salt in the water should help i wouldnt worry about the spots. wiki marimo and read the article very carefully there is a lot of info. i think thats where i heard about the salt.



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