Michelia maudiae is hardy; my plant does find in 30 degrees temperature, sounds like the pots were too dry which in some cases will cause them to shed their leaves.
Dick Figlar of the Magnolia Society did a hardiness test in the winter of 2003, in his e-mail he stated the temperature was 5 to 10 degrees F "Slight Leaf Burn-just a touch of bronzing on some leaves, otherwise seem fine"
Cal

Plants in pots are MUCH less hardy that those in the ground, as roots are often quite tender--especially immature roots. Immature roots of otherwise very hardy star and saucer magnolias have been found to be hardy only to temperatures in the mid-twenties Farenheit.

I bought a Michelia maudiae (now classified as Magnolia maudiae) from Nurseries Caroliniana two years ago and it has been in the ground since then. It has survived in north Georgia with temperatures down to about 15 degrees with no problems. It was about 2.5 feet when I bought it and is now over 10' tall. It is evergreen. It is in some shade and hasn't flowered, but I've seen plants in flower and it is awesome. I wonder if you may have gotten an Michelia that was mislabeled. I had a few two years ago that all bit the dust when frost came around.

Hardy isn't the same thing as evergreen, of course -- many broad-leafed evergreens will drop leaves if it gets close to their hardiness limit, and if the plants were wet and cold, that could cause leaf drop as well as root rot. What BBoy said is right, a young plant with a small root mass, constricted in a pot, isn't nearly as hardy as a mature tree in the ground; the rule of thumb is at least 2 zones less hardy.

This species is pretty new to this country, so even expert growers are still figuring out how it does in various American climates. Magnolia family plants in general have fairly sensitive roots that stay near the surface, so they need mulching and special protection the first few years.

Don't water them too much while they're putting out new leaves, but give 'em as much light as you can, and maybe you'll be rewarded with early flowers, and then you can put them in the ground in spring!

Jim

I planted a 2.5' M. Maudiae four years ago and it is the highlight of my garden and stands at 12'. I can't believe the growth rate for a Michelia and the beauty and fragrance of the flowers is outstanding. It is in very organic moist soil and gets full sun in the morning and part shade in the afternoon.

My experience with Michelia (I grow maudiae and figo)in general is that they tend to drop their leaves when the roots are disturbed. All my Michelia, including the maudiae, dropped ample leaves if I put them in the ground. In the last four years my Michelia all experienced unprotected lowest temperatures of -11.5C and -7.5C. I lost five of my six containerized figos (only one left but it seems fine although it lost a lot of leaves and growth) but the maudiae has been untouched - not even leaf drop. Maudiae hardiness is not an issue in my zone to date.

I went to Stephen F. Austin's Mast Arboretum last night and saw one of these michelia's blooming. It was wonderful! The tree was around 25 ft tall, not a shrub at all, and was evergreen, with these big white flowers on it. The flowers had a fragrance that I can't describe, kind of like gardenia. The fragrance perfumed the whole garden. I am so excited about this tree and the fact that it blooms in January, when the rest of the world is so gloomy. This is a must have plant for anyone that enjoys fragrance in their garden. It may be my new favorite plant.