I have grown some plants in alf249's Succulent Planter Cube (https://www.thingiverse.com/thing:3646868) and the plants have outgrown them. I've scaled that model up to accommodate, but I needed something on the order of 100mm and scaling that large meant the walls were bigger than they needed to be. So, I created a new version from scratch with alf249's model as inspiration.

I made the walls considerably thinner and I think I rounded the exterior corners a bit more.

There are no drain holes, so be careful what you plant and how much you water.