Will not necessarily always be produced using same propagation method throughout industry. The way to check if yours happened to be grafted would be to examine it. There should be some sign of a graft union. Rootstock suckers might also produce quite different leaves than the 'Merrill' scion did.

Thing is, if it froze to the ground once...

Any named magnolia variety from a reputable nursery would have been grafted or budded - seed propagation would be very unlikely to produce the true Merrill. If the suckers are coming from below the graft union or bud site, they are not Merrill, but whatever root stock (usually m. kobus)used.

If you had an exceptionally cold winter or the tree was stressed from another cause or was sited in a very windy location, the Merrill portion may have been killed. This is, however, an extremely hardy variety. If I remember correctly, it has bloomed after -35 at the U. of Maine garden in Z4 Orono.

Cuttings are also used.

... and are frequently preferred!

FWIW, we planted one of these in our front yard when we lived just south of the Twin Cities. It was in a fully exposed location with no winter dieback in the 9 years we lived there.

The only problem we experienced is that the trunk split open one winter, but healed in time.

My only other complaint is that it was a fairly slow grower-it averaged around a foot per year, maybe.

Overall, it was a great tree I'd recommend for Z4.

I realize that doesn't directly address your issue. I just wanted to throw in my experience with it.

Thanks for the input everyone. I have dug around the truck and can't see a definite graft line. The nursery where we got it just said that the suckers would grow into a tree and flower--eventually....no answer on the grafting issue. The tree was doing great last year and set lots of buds, but we did have a really tough winter with unusual winterkill on some of our junipers etc that normally are just fine. So I guess I'll just let the "little suckers" grow and pick one to keep if they make it through the coming winter.

I contacted the nursery again and was told the magnolia was grown from a cutting, so the shoots coming up will be the Merrill variety. So we will just wait and see what happens.