For those talking about attempting to grow items one zone colder than
recommended for any species, listen up. That's what I do and here's how I
do it: At least one seed out of 1,000 should produce a plant that will
thrive in one zone colder. And, at least one seed in 100,000 should produce
a plant that will thrive in a two zones colder climate.
I produced/invented the Pequot Black Raspberry, a zone 3 plant, from
hundreds of thousands of zone 5 black raspberry seeds.