I go there quite often and have never seen them planted outside overwinter. They do have quite a variety, especially around the Conservatory, but no Southern Magnolia... I have seen them plant exotics, palms, but only for the summer.

I do grow Southern Magnolia, I am near O'Hare... it's been growing for four years and now it's the tree's third winter. Last winter and right now I use no protection at all, it loses some leaves from winterburn, but it grows bigger and better every spring.

Below is a link from its second year growing... I should get some recent ones.

Here is a link that might be useful: {{gwi:1053281}}