The Plant Support Ring design is used to hold succulent cuttings upright for rooting. It can also be used to support seedlings that are too weak to stand upright. 

To use the ring for rooting cuttings, press the two halves of the ring together and place the ring on top of the potting soil. Place the cutting upright inside the ring with its bottom on the soil and add a small amount of soil to the ring to stabilize the cutting. The elevation of the ring will help to keep the succulent cutting from getting too wet and rotting. After the cutting has rooted and grown out some, pull the ring halves apart to remove it without damaging the plant.  
 

Printing:
I printed this design using generic PLA filament and the default 0.20mm Standard settings in Creality Print 6.0. No supports are necessary.
You can scale this design in your slicing software to print whatever size you need.