- Dec 2015
The impression is that "Indians" for Native Americans is a misnomer; it would be more accurate to call them by their group names.I don't know about older varieties of corn, but modern varieties of sweet corn can be harvested in 60-90 days.
Of course, the Indians didn't have modern varieties. So it's hard to tell how far north they could grow corn.
For example, the Quechua is known to have many varieties of potatoes:
The 3800 Different Types of Peruvian Potatoes - LimaEasy
The Irish famine was caused by monoculture: the farming and dependence of one variety of potatoes.
Why didn't the Irish adopt more variety of potatoes?
While China is not the home of corns, it is home of glutinous or waxy corns:
Waxy corn - Wikipedia
Why waxy corns are hardly grown in North America?