If you’re concerned about flashing the candle wax, place the candles in fire resistant glassware such as small Pyrex dishes or other container. I would only ever use one candle per flower pot.If you leave the hole open at the top, most of your heat will still go straight up to the ceiling. Place an inverted clay saucer on top. Then ALL of your candle heat will heat the pot which is the entire concept behind brick ovens. It will get too hot inside the pottery and/or it will snuff the candle if you don’t have enough airflow.P.S. Too many candles in the room will deplete all of the Oxygen as well as raising the CO2 concentration to unsafe levels.