After printing many self-watering planters plus inserts, the most time and resource intensive component was the pot itself. Finding a cheap and environmentally friendly pot, however, was super easy in many hardware stores, garden centers. 

Many inserts would be suitable with a little scaling, but I wanted something a bit better fitting, so I created an openscad script to fit almost any pot size, and allow for pots that are shaped wider towards the top.

Customizing your insert

This uses the OpenSCAD program to generate the stl file. Customize variables within the script to produce a self-watering insert that meet your requirements.

The script has 5 variables at the top:

container_radius_top  : This is the radius as measured from the top in mm.
container_radius_bottom  : This is the radius as measured along the bottom in mm.
container_height : This is the height of the pot in mm.
wall_thickness : This defines the thickness of the insert wall in mm. This is measured inwards so will not affect the overall radius or height of the finished product.
print_indicator : set to true if you wish to generate the water indicator as well. the water indicator can be separated in prusaslicer. Requires styrofoam or similar to allow the indicator to float on top of the water.

If your pot has no angle and is straight up and down, simply set the top and bottom radius to the same value.

Printing

I have tested prints of the insert at .3 layer height with PLA and without supports.

The script generates a water indicator designed to fit inside the spout. This part will require supports and should be printed upright due to it's shape. This will need to be separated in the slicer if you wish to print it a different color without mmu. Use prusaslicer's “Split to objects” function to do this.

Export as an STL from openscad, and open in your slicer of choice. 

The script produces a water indicator that fits inside the spout. 

Inserts designed for pots with a significant difference between to top radius and the bottom radius will require supports. The spout should continue to work, but likely the water indicator will not.

Water Indicator

The water indicator will need to be attached to some packing foam or Styrofoam to allow it to rise with water. Glue with super glue or wood glue.