They grow fine here in zone 6 and they have taken -15 to -20 for short durations. In your zone though I would plant it in a location protected from winter wind and direct all day sun. They also seem to become hardier and look better after they get established so I would baby it for the first 2 years. Wilt-proof might also help while it gets established.

If your in an area thats gets into the -20 range for extended periods of time or much below zero with lots of winter wind you might find it difficult to grow. No matter what you do though you will never have a tree that looks like the large ones in the south. David

USDA 6 is the lowest of the comparatively mild zones, when you get into Zone 5 you have crossed a line. An inherently southern tree like Magnolia grandiflora will definitely be beyond its normal parameters. An extra hardy selection may grow for awhile, if you don't need it to live for decades you may wish to plant one--in a sheltered position.

I'd encourage your wife to learn to love the wide variety of trees that thrive in that area, rather than try to coax a Southern lady to shiver in a Northern winter.

BBB has been widely-planted on the U of MO campus, in Columbia, MO. Some in protected spots, others in fairly exposed locations, and all appeared to be doing fine when I was there in the early 90s - some years, there'd be quite a bit of winter leaf burn, but all in all, they seemed to be OK. Some were pretty large.
It'd be worth a shot, but as bboy indicates, it may not achieve the glory of a MS-grown tree.

There's supposedly the edith bogue cultivar that was developed in NJ.

While more hardy than usual 'Edith Bogue' is apparently not the most hardy and definitely not the most ornamental of the hardier selections. It originated in Florida, came to notice for surviving in New Jersey. It has an average appearance for the species, with a somewhat open habit and some indumentum but not alot, this often becoming thin as the leaves age.

I'm trying to think of some other 'Southern' trees that might be more adaptable to a zone 5 location. (BRRRRRRR) That's quite a stretch.

Oh I might have been thinking of the Edith Bunker cultivar. Nevermind.

I say try it with a small tree the worst that can happen is it gets really big then dies on ya.

I know BBB was field tested in southern PA. It survived -22 F with out a single leaf or bud dying. As noted in above posts, longer exposure to lower temps can minimize ability to winter well, as can a lot of wind.

I don't mean to be a pain, but you do know there are a lot of other magnolia species and varieties out there? You could spend a lifetime trying them all and not fully get there.

I'd suggest the Southern Magnolia cultivar '24 below'. It seems to be the hardiest cultivar and it's foliage holds up much better than BBB to cold winter wind and sun(then again 'Edith Bogue' also has it's foliage hold up better than BBB). I'm in zone 6 and grow all of the so far mentioned cultivars and '24 Below' has never had the slightest bit of leaf burn and is growing like the large Southern Magnolias you see in the deep South so far, unlike BBB which is a smaller upright shrubby thing. Although I think you can't go too wrong in trying either of these cultivars. The worst thing that could happen is they could die back or die on you.

If I were you, I would plant the tree in an area which gets the most wind protection you can give it and doesn't receive any mid or late day winter sun, but gets at least some full sun during the summer. SE exposures or under large high trimmed shade trees seems to be best for this. Good luck!

The S. mag cultivar "Victoria" is doing well for me in a badly exposed spot -- now 6' tall. It suffers less visual winter browning than nearby Thuja "Green giants". It seems to want to bush outward a bit compared to the usual -- this is what I wanted.

I moved up North 40 plus years ago from North Carolina.
I currently have 5 cultivars of Magnolia Grandiflora.I have
provided cutting to Dawes Arboretum where they are out in the
open. My Brackens is about 40 feet tall and blooms heavy every year. It is sheltered from SouthWest Winds. That is important.
If you can get it established for about 4 or 5 years it should do fine. However we have not had Zone 5 winters in Ohio for 10 years. Good Luck

Little Leaf Cucumber Tree (Magnolia acuminata) does very well in Zone 5 - I've had very good luck, but they are rather large trees. Also had good luck with some smaller cultivars - Alexandrina, Jane, Ann, all Magnolia x soulangiana cultivars. You may be able to use some varieties that are not as cold hardy if they are sheltered.

Joseph Hickman, a well-respected attorney (now deceased) formed his own club of hardy southern magnolia fanciers. His collection of magnolia grandiflora and american Holly still is in Benton, Illinois. In his opinion Brackens was the hardiest. I have done numerous google searches and found many are growing it west of Chicago. Many years ago Dr. Dirr did an article on testing the limits of southern magnolia in the Horticulture magazine in March of 1992. He did a very scientific study and rated some of the hardiest magnolia grandliflora known.
In my modest collection I have Edith Bogue, Twenty Four Below, Victoria, Poconos and I had a nursery in Tennessee to root some cuttings from the most exposed of locations that fared the best in winter of the late 70`s here. If everyone was contented with the plants as they were originally where would we be today. People like Mrs. Meservae I`m told wasn`t contented with what she hollies she could grow. With very limited knowledge of genetics, she still made quite a contribution to plant lovers everywhere with the blue hollies rugose/Chinese hollies and rugose and English Holly. I don`t think one should stake their livelihood on growing plants of marginal hardiness, but pushing the limits benefits us all. By the way there are also evergreen forms of magnolia virginiana. I`m experimenting with Henry Hicks
Pat McCracken has it as one of his goals to find or create selections of magnolia grandiflora for Zone 4.

Well, I hope Pat McCracken gets his zone-4-hardy Magnolia grandiflora, and soon. I am not getting any younger and I need to plant a M. g. very soon. (:o)
Mike

There is some breeding work going on crossing the hardiest Grandiflora with the Hardiest Virginiana that may Yield a zone 4 hardy evergreen magnolia. It will be interesting to see if a plant that can withstand a zone 4 winter looks very attractive after it. After seeing the leaves on my Henry Hicks, the plant may look better if it had dropped them. David

Not a 'grandiflora', but isn't there a Mag. virginiana var. 'australis' for zone 5 that is considered mostly evergreen? I suppose it might lose leaves in upper zones.

dave_in_nova, that cultivar of M. virginiana var. australis would be 'Henry Hicks'. There's also 'Satelite' which is nearly as hardy and another new one that many are pushing as being very hardy which is 'Jim Wilson' (aka Moonglow) selected by Earl Culley in Jacksonville, Ill. It's been reported as hardy to -35°F(-37.2°C). Although it's not always completely evergreen in harsh winters.

"Alexandrina, Jane, Ann, all Magnolia x soulangiana cultivars..."

Alexandrina is a cultivar of M. x soulangeana(it appears several different cultivars of M. x soulangeana are being sold as 'Alexandrina' in the US), but 'Jane' and 'Ann' are part of the "Little Girls" series of hybrids released by the National Arboretum and are hybrids between M. liliiflora x M. stellata and are not M. x soulangeana(which is M. denudata x liliiflora).

I live in central Illinois at the border of 5a/5b. I have a BBB growing on the northside of my house. I planted it in the summer of 04 and it has done great actually here. I do lose leaves towards the end of winter but even after several weeks of sub zero weather this past winter my magnolia still had most of its leaves. Browning didnt occur until it warmed back up. I still had leaves at the end of the branches and no damage to wood. I took a different route rather than protecting from wind, I protect from winter sun. It doesnt need direct sunlight if its really cold out, the plant wont want to be forced into too much thinking. These low temps in the winter of 06-07 were during a period of strong winds and blizzards. This spring it flowered well and few nice and green. -7 is the lowest temp weve seen here in over 10 years. Probably 1994 was the last severe cold snap where we did actually get to -12 below or so. I know others that have had relative success with Edith Bogue and BBB here in central Illinois. I kind of get confused by all these super cold temps down south I heard about over this past winter because we didnt get as cold as they say they did down there. Mother Nature never surprises me though completely. Temperatures have been warmer in the last 30 years than previously. Ive seen full grown Mimosas in some peoples yards, not that it would take them long to get there.

Ik this is old, but for a southern tree for zone 5, bald cypress would definitely thrive, they are zone 4 hardy