They don't mind cold nights at all!
Eventually the lack of daylength will slow them down.
The people at the Roughwood seed collection were trying to select a hybrid they were breeding for cold resistance. They HOPED to work it up to the point where it could overwinter under plastic in their Zone.
The breeding program was cut short when they noticed that a few seeds had escaped the plastic-covered breeding area. They were growing happily without ANY cover, over-wintering without a care and coming back in the spring. Shouldering the competition aside.
"We don't NEED no stinkin' breeding!"
