Hmmm, interesting. Never tried it myself, Jeff. If you decide to experiment, definitely let us know how it turns out!

I stopped using a "drainage layer" 20 years ago, except in a few bowls/jars just for looks.

Drainage layers are useless in both pots and terrariums. Worse, they can collect stagnant water and cause more problems. Using a non-absorbent layer of something like aquarium gravel can even cause the soil right above it to remain saturated, without draining excess water, due to the surface tension of the water and hydrophilic nature of the wet soil mix as opposed to gravel. This invites root rot and/or weak, shallow root systems.

A well draining mix all the way through will do just fine.

Underlying mix that drains even better but still wicks moisture (like the AV wicking mixes) will do equally as well. I often sprinkle in some charcoal too, roots do seem to like it, but only a thin layer that mixes in with the soil mix.

If you must go with a layer of gravel or whatever, for looks, just be sure you're not leaving stagnant water in it between waterings. Or put in an aquarium airstone and keep it aerated and alive. (joke - sort of!)

Vincent

Thanks Vincent!

That makes sense and is much more attractive than a drainage layer... even if i use black stone that matches the soil, it is still noticeable.