How to set padding between columns of a JavaFX GridPane?

For better appearance you can use a mix of:

grid.setHgap(10); //horizontal gap in pixels => that's what you are asking for
grid.setVgap(10); //vertical gap in pixels
grid.setPadding(new Insets(10, 10, 10, 10)); //margins around the whole grid
                                             //(top/right/bottom/left)