Don't plant them into the ground until ALL danger of frost is over. You know your area for that.

If you want them to bloom as early as possible, I would give them an early start in a large pot. What I did with mine ( zone 5), is pot them in a large one or two gallon pot ( dependent upon the size of the tuber), then put it out on warm days, but at night I carry them back into the garage. They don't like the cold, but would benefit from the time to form a good root system.

..... just my humble opinion.