I uploaded both variants either to mold or just print the planter.

If you want to mold it use fine concrete or plaster for the perfect result.

To get great results I recommend printing the mold with PLA because of its thermal properties. 2 perimeters/walls should be perfect. For a clean finish print with 0.1 layer height, use leveling compound and get all the bubbles out of the mold.

To release the molded part after curing ( i recommend at least 2 days of curing) seperate the two halfes the pice will come out easyly. To prevent crumbling use some layers of water-resistend clear coat to protect the concrete.