The clock itself, excluding the electrodes and wires, is made of bamboo, which is an extremely renewable, sustainable material. And unlike some science-project-type timepieces (we’re looking at you, potato clock), this one is actually quite attractive. You just push the zinc and copper electrodes down into the dirt of your two potted plants and make sure to keep those plants watered. Just don’t use vegetables or herbs: the zinc electrode degrades into the dirt in time and you don’t want that coming up in your tarragon. You can make your potted plants finally pull their own weight in your house for less than $40.