There are there models to print each with different diameter.
You can also edit the diameter with the openscad file.
After printing the lower part with the water reservoir was coated with polyurethan (nail polish fixer). This was done because of previous fails and leakages.
The thing was derived from some NASA paper which states that the roots of the plants are cleaning the air.
You also have to mix the soil of the plant with char coal.
So have fun with this thing.