Very large, Cookygirl! They will need a tub at least 1 meter wide, and 70 cm deep.

I used to grow sweetcorn in gro bags. I would get 1 bag for 2 or 4 plants. Fold the bag in half, stand the two ends together, and cut the top of the fold, so it ended up like saddlebags, plant into the top, make small hole for drainage. or use 5 1' diameter pots. Fill with grow bag comtents, water daily and feed twice weekly with tom fert or similar.

Don't skimp on the fertilizer, too. One reason I prefer the big tub, is to give yourself a little more leeway. A starving corn plant is just a big weed!