I live in Missouri and Magnolia tree us brown and the leaves are falling off like I have never seen before.
Is it because of the winter we had?
I'd guess so. My Little Gem cultivar is doing likewise. A guy up the road has two good sized magnolias (I'd always assumed regular 'ol Grandiflora just 'cause of how large they wereÃ¢ÂÂ¦ probably 40' at least). They're dead as doornails this spring--really sad. I can only assume that whatever cultivar they were, it didn't like a couple weeks in the single digits.
But to answer your question, so long as the majority of the leaves are still green--and assuming you don't have any sort of insects and/or disease--I'd attribute it to the winter and not worry too much. That's what I'm doing, anyway. ;-)
Look for swollen buds. My evergreen Mags have shed their leaves, but have swollen buds, for new leaves. If there are no swollen buds, sorry but it's a goner.
I presume you mean an evergreen Southern Magnolia? (Magnolia grandiflora)
'Little Gem' burns in my part of Zone 8 so I would certainly expect damage in Zone 6..
I am in Ohio and so I assume we are both around the same zone. This is the northernmost limits for most Magnolias, esp. M. grandiflora. This winter was just too much for many of them.
Your Magnolia may leaf out again. Many trees can and do leaf out after their foliage has been killed by cold. You will have to wait and see.
Famartin, I mean Mag Grandiflora, the regular southern Mag, and my Brackens Brown Beauty. The Bracken's brown's buds got ugly over the last evening or 2. I think it will be fine.