I cat proofed my balcony last year, and for achieving that, I had to fill those big pots with concrete to create the fundament for the rods, that hold the net.

I covered the surface with decorative white stones, and it looked fine.
... for 5 minutes.

Over the summer, it filled up with algae, and probably quite a lot of mosquitoes too, because there was no drainage.

So, I decided to make the best out of it, and turn it into a bog garden!

I replaced the stones with leftover lava rock and LECA/ pon, so I get a airy, but well wicking substrate that plants love, while covering it fully, so no mosquito larvae can live there.

I let it soak in the rain water for a few months now to get rid of any salts or fertilizer left, and also transfered a Sarracenia (carnivorous plant) to the new substrate.
The roots looked like this today while repotting it to the big container:

Today, because the weather was great, I also walked around my neighbourhood and collected some different moss types from different environments.

They mainly serve as water purifier and filter, so when organic stuff (flying seeds, insects, etc.) lands in there, it doesn't rot, but gets decomposed and eaten by the moss.
Also, it hopefully prevents the salt crust build up I usually get with hydroponic media, and also prevents it from drying out or algae growth.

I'm also trying to grow other cold resistant carnivorous plants, like a few different other Sarracenia types, sundews and the obligatory venus fly trap, a few of which are native in my area.

They hopefully will get rid of some insects I had to fight with last summer, like wasps, flies or other annoying critters.

I currently have 5 of those containers, and besides the one I already showed you, one other is also treated similarly, but kept dry.
I try to turn it into a stone garden, with mainly succulents growing there.

The bog garden will only very rarely get drained, if at all, and the other one more regularly. Hopefully, some other native hardy species will come there and colonize the pot.

If it works out well, I will turn the other 4 "decorative" ones into similar environments.