The reason nobody answered about Nebraska is probably because nobody from Nebraska noticed the thread. But really, this isn't hard for either one of you guys to find out. You don't need to ask marijuana growers. Just call up your local garden store and ask them. Tell 'em you're planning on starting your tomatoes indoors this year, and you're wondering when it's safe to put them outside. They'll tell you when the average last frost is in your particular area. "The Midwest" is just too big an area to be covered by one answer, and actually the same is true for Nebraska. I'll bet the last frost date in Nebraska can vary by as much as a week and a half, depending on how far north you are.