Love this tree. Standard (non- chocolate) grows well here in western/coastal michigan. Have also planted chocolate version in a somewhat protected area. Growing slowly so far, but bought a small one. Figure it will take off this coming year. We are in zone 6. Also grown in columbus ohio which is also zone 6.
Aside, reading "The Splendid and the Vile" about Churchill/WWII. When London/natural history museum was bombed/fires put out with water, 147 -year-old seeds germinated and started to grow.