Depending on crop you can go higher than four pots. Verti-Gro carries an extension pipe for the tower that will let you go 7 pots high which is what most of my towers are. What are you growing the corn in? I'm using 7 gal pots and plant 6 stalks per potI'll post more pics when the big garden gets going. I bought my stack pots off the internet, craigslist. Verti-Gro has a web page and the people are really helpful. It is a great way to garden. I will end up with about 1000 plants in a space of about 600 SF. Growing upwards is a great way to do it.
pictures are mandatory.....We are currently fully engaged in getting the "real" garden laid out and set up. About 24 tomato pots, 12 corn barrels, 40 stacks of four pots on a grow bucket.