EDIT: I no longer think this is a good design, as it promotes mold by constant immersion. I think a design which uses some type of a water wick would be superior.
Designed for a mason jar exactly 7cm wide inside brim, which is the standard "wide mouth" mason jar. I think this will fit a few mason jar types, including the wide body one you see in the photo. Planter reaches 145mm down inside the container.
Material: I did it in ABS because I had extra and it won't decompose. Would probably be fine in PLA but I don't know how it would hold up after a year, since PLA is a tiny bit biodegradable if wet and in the sun