My daughter recently brought home a science project... a sealed ecochamber, made of 2 soda bottle bottoms, one inverted to fit inside the other. The chamber was filled with soil and plants. Despite its green plastic ugliness, the plants lived happily for weeks. The idea was simple. Plants give oxygen. Bacteria in the soil gives carbon dioxide*. Water cycles through. Trapped inside, is a whole little world. No need to water, at least in theory. In real life though, the water level needs to be checked every few weeks.
We decided to take the same idea, and make an ecochamber of our own, otherwise known as a sealed terrarium. We used a glass canister and put some rocks in the bottom for drainage, a layer of activated carbon (optional) on the next layer, and finally, some potting soil. Then came the fun part – planting. We added just a little water. If you add too much, just leave the lid off for a day or two.
The Corsican Mint has a wonderful scent when we open the jar to check on our little world. The tiny Rabbit's Foot Fern adds a bit of height. The Blue Baby Tears have miniature blooms for color, and the pincushion spikemoss, well, I think moss is a requirement in a little terrarium like this, and for some reason, it's my daughter's favorite.
* To make a completely sealed terrarium work, you would need an animal to provide carbon dioxide. See here for details. With its removable lid, ours is only partially sealed. And no, I don't recommend adding any critters to the terrarium.