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Marimo: “Houseplant” for the New Generation

one small Marimo to take home, with googly eyes attached

Usually when I see or hear of something three times in a row, it peaks my interest. Recently I had seen images of Marimo on Facebook – green, moss-like balls in water. Last week, City Planter, a local plant business, was selling them at the Philadelphia Flower Show in water-filled plastic pouches. I did not buy one but I thought it would be a great gift for my kids as they move into college dorms this fall. This week, I received an e-mail from The Sill announcing they have Marimo as a “houseplant” in stock again.

Marimo are balls made up of green algae (Aegagropila linnaei). The algae is a filamentous form where the filaments grow out from the center in many directions. The rolling nature of the water in the lakes in which they are found mold the algae into spheres. This filamentous algae is found only in a few lakes, one of which is Lake Akan in Japan. Marimo is the Japanese word for the balls.

Marimo grows slowly, just a few millimeters per year. They are long lived in their natural environments, lasting over a hundred years and reaching a foot in diameter. The Marimo balls that are sold as “houseplants” are juveniles, only a few inches in diameter.

Marimo can be kept in glass bowls by themselves or in aquariums. However, some fish such as goldfish eat the balls so check with your pet store first. The balls photosynthesize just like a houseplant and prefer indirect light or aquarium lights. If separated or torn apart, they will not die. However, you may have to hand-mold them into balls again. They cannot be allowed to dry out or they will die.

individual glass container of one Marimo to bring home

In nature, Marimo are spherical because of the lake’s rolling water but in a glass tank they may lose this shape because the water is still. Simply hand roll the Marimo to retain the shape. This also allows other sides to receive light evenly. Because they come from cold lakes, they prefer cool, clean water which means the water in the glass bowl cannot be allowed to heat up (which will happen with sun or direct light) and has to be changed every two weeks.

Theoretically, Marimo balls will outlive you if you treat them right. Not like the goldfish I got for my kids when they were in elementary school. In the fall, as my twins head for college, I will buy them glass bowls of green Marimo balls, the low-maintenance “houseplant” for the next generation.

holding tank of many Marimo for people to purchase individually