Alcea nigra grows to about 6feet, so may look a bit odd in a tub, maybe a better option for a tub would be, "majorette" which is a dwarf variety, and only grows to about 3 feet, comes in various colours, inc yellow, carmine-red, and yellow, but both are only short lived perennials. Derekm

If its is big enough then yes. But it will be at greater risk of being blown over, so lots of 'weight' in the tub.