A cheaper alternative to activated charcoal for your terrarium

Terrariums have taken the horticultural world by storm over the past decade or so, going from obscure Victorian curiosity to a staple of homeware stores. Yet in almost any advice you will find on how to set up one of these miniature gardens in a sealed glass container – be it online, in books or through in-person courses – you will come across a tip to include activated charcoal in your potting mix.

This substance is more easily tracked down as a fancy food supplement. It can sell for pretty exorbitant prices and is often described as essential to creating a functioning…