Here are some modern wall planters I designed and printed in Bambu Lab's marble PLA as well as terracotta PLA on an A1 printer with a 0.6mm nozzle. They mount to the wall with two screws for, they are well-secured and so far they are holding up great :)

They have removable inserts with drainage holes so that you can easily take the plants out, water them, drain them, then set them back in the wall planter. The large insert is 1.2mm thick so that it prints relatively quickly while remaining quite strong. The smaller insert is 0.8mm thick for printing with a 0.4mm nozzle. 

Note for printing the inserts: If you do not have a printer with an temperature controlled enclosure, there will be some warping on the inserts due to their large thin surfaces. To fix the warping after printing, gently heat the warped portion with a hair dryer/heat gun and press it on a flat surface to flatten it out.