I have an Ikea Gersby shelf and devil's ivy plant. These brackets allow to mount them together.
Gersby is made from MDF of 3 different thickness: 18, 19 and 20 mm, so I made all 3 sizes. As a bonus this made brackets compatible to almost any shelf. You just have to print bracket, add a piece double sided tape (foamed will work best), and enjoy your plant!
Any plastic will work