Another option is to leave the column as datetime, but only show the date part in the data grid. It just depends on whether you might want the time portion for use somewhere else or not.
To do that, drag a label onto the column in the row template and bind the text field to
self.item['created_on'].strftime("%b %d %Y")
Adjust the format to suit what you want displayed, and change the field name to your column name.