When I was doing my pottery apprenticeship in Minnesota in the early 1980's I began to explore how to alter thrown pots to have facets, created with a flat rib just before taking the pot off the wheel. I think this form works well for a flowerpot!
#2 Faceted Flowerpot
5" Tall X 5.5"Diameter
This pot was fired to 2000 degrees fahrenheit, but care should be taken to not leave the pot outdoors in freezing temperatures.