Chinese Toon Hardiness

I was just wondering if you might be able to help with a question I have about the Chinese Toon. I recently ordered some seeds from you, and was wondering if the trees would be able to be grown fully outdoors in my area. I live in zone 5, and most websites I've looked at say they are hardy to this zone, but on the back of the package it is noted that they are tender perennials and must be brought in during the winter. Is there something I could do to make sure they grow well outside and will not die back in the event of a late frost or "false spring"? Thanks so much!

Chinese toon (Toona sinensis) is relatively new to North America and I don't feel that there is enough of a body of experience with it to be able to say for sure what the hardiness zone range is. Some sources say it is hardy down to zone 5, others say zone 6, and some say zone 7. Although we are located in zone 5 we have not attempted to winter it outdoors, so we have no direct experience on which to base our own zone ratings. For now, we have put the hardiness zone ratings for chinese toon to 6-9. That would make it a tender perennial in zone 5. It should be pointed out that even if the plant is hardy in zone 5 that does not mean it will grow into a mature tree.
The plant is frost tender so one has to be careful not to so the seed too early if sowing direct outdoors. Because the plant is now grown as a "micro herb" for the fresh herbs industry we have given it a sowtime code "X" which means "anytime". But this does not apply if you are growing it to be a mature tree; for normal (i.e. non-"micro-herb") purposes you would sow the seeds in spring for spring planting outdoors.