For what it's worth, I have grown corn in an Earthbox, which is only about 3 ft long x 18 inches wide and only about 1 ft deep. There were about 11 or 12 plants in the box in two rows. These were a shorter variety, but each plant produced 2 ears (and they were quite good). However, Earthboxes are designed to provide a constant supply of moisture and fertilizer that a simple bucket doesn't really replicate. But I've also started them in pots in the greenhouse and transplanted them with no problem.
Not sure if any of this is relevant to your situation, tho.
