The whole idea of a bottle garden or terrarium is that it forms its own micro climate. This is created when the moisture in the compost evaporates and then condenses on the side of the bottle to run back down to the compost re-watering the plants. This is possible because there isn’t any drainage holes in the bottle or terrarium. It is possible that the compost can become ‘sour’ and smell badly. By adding charcoal to the compost at planting time the compost is kept ‘sweet’ due to the filtering action of this activated charcoal.
This container will be sufficient for many bottle gardens and terrariums.