This is one of my older terrariums in a wine bottle. It's lasted for about a year and has really filled in. In this photo you can really see the layers of gravel, charcoal, dried moss and soil in the bottle.
My sister has been asking for a terrarium for ever now. I was hesitant to give her a terrarium that hadn't properly settled for fear it would dry out or die or get diseased. However as this one has lasted so long I am proud to give it to her.
The sword fern [nephrolepis cordifolia] is doing so well that runner plants are growing off the parent plant and on the side of the bottle. Some of the older fronds are turning brown and dying but I think the decomposition will not harm the eco balance in the bottle.