corn doesn't take up a lot of room. you're best to plant it in blocks though, rather than rows - it makes for better cross pollination. ideally, for the varieties you can buy locally, they need to be about 9 inches apart - we tend to plant a row, offset the next row (so they are only about 5 inches apart) and then plant the next row the same as the first. never had a problem with them
with watermelon, rock melon, pumpkin and cucumber, we plant them on the edge of a raised garden bed, and as they grow, encourage them into the grass. that way, the root system is protected, and it's only the actual plant that has to spread out. it should be ok to let it take off. DH won't let me have any melons this year though - says DD is too young to understand if she loses part of her yard to fruit plants that are creeping, given it's not a huge yard like we used to have. i REALLY want to plant pumpkin too, but he said no. tempted to just get a pumpkin seed and stick it in a pot, and if it takes off, so be it - i'm sure she'd learn to live without that bit of room lol

