I certainly wouldn't plant them any closer than 10". If you try to cram too many plants in there, they won't do well and may not make ears. Even at that spacing, be sure you are really on the ball with watering -- tightly packed plants and drought are a recipe for failure.

Both of the kinds you are planning are normal, open pollinated corns, so they don't have the issue of making "flinty" kernels like some hybrids can when different classes are planted together.

In theory, if you were to plant them about 3 weeks apart, you probably could do what you are planning and get relatively pure seed from each strain. However, I don't know if it works differently in Arizona due to climate, but here in Michigan, it seems like staggered plantings all seem to mature at about the same time anyway -- probably a function of our cool springs where the early plantings just sit, and then all start to grow when it warms up.

With the planting density, I don't think you should have any problems with pollination, but OTOH, with such a small bed, it sure wouldn't be very hard to do some hand pollination, so it might be worth the few minutes work just as an insurance policy.

here in virginia staggered plantings tend to all get ready at nearly the same time as well...

Plant the second planting when the first is about 6 inches tall. This will give harvest about 2 wks apart. To get even spacing on harvest you must stagger planting by size of the previous planting(the country farmer way) or growing degree days(the scientific way).

No matter when you plant them you will be running a chance of cross pollination if they both have tassels at the same time. I would not plant them together if I wanted one for a pure seed strain next year.

Thanks for all the replies, I've decided just to plant Black Aztec this spring and do the Bantam in the fall, I'd rather not take the chance of cross pollinating and given that our seeding window is so short in the spring, I don't want to leave the second planting to late.