I'm no expert on magnolias (I rather hate them, actually, due to many childhood hours wasted raking tens of thousands of their leaves and picking up their horrible seed pods) but that doesn't sound right at all.

First thing, was it root bound when you planted it? If the roots were all tight and balled up in a small pot, then often that tree will get permanently stunted because it can't develop a proper root system.

Barring that, are you fertilizing the tree and ensuring micronutrients are available? And is there grass growing underneath the tree? St. Augustine grass in particular will gobble up every bit of water and nutrients and not let the tree get what it needs to grow. What about soil conditions there? Is perpetually wet or dry? I wonder if pH makes a difference for these trees.

Are you sure you don't have a dwarf " Little Gem " magnolia tree ? What about the beautiful white flowers in spring,..none of them either ?
I have two on my front lawn, one a " Little Gem " and the other a normal Southern Magnolia. The Little Gem was 3 1/2 ft tall at planting 3 yrs ago and now is 6 ft tall. Am expecting it to top out at about 9 - 10 ft. I have given it lots of TLC,..watered it 2 x a week the first 6 mos, then only occasionally, but fertilize every 3 mos with 10-10-10.
I love magnolia's, the normal Southern Magnolia ( will get to 60 ft ) is now a robust 7 foot tall with the most magnificently scented, foot wide white flowers I have ever seen or smelled.
Perhaps yours is a " Little Gem " dwarf and maybe even damaged somehow,..no growth in 6 yrs tho is very strange, even for a Little Gem. I'd ladle in some 10-10-10 every 2 months and carefully water it. If still no sign of growth I'd think seriously of digging it up. Good luck !

Thanks for the replies. I'm pretty positive I "loosened" the root ball before planting it. There is no grass around the tree (it is surrounded by a 6 foot circle of mulch). It has bloomed every year..big beautiful white flowers which smell lovely. The leaves are nice and shiney. It's just not getting any taller. One thing though.....it WAS planted on the site where a deceased Sago palm tree existed. I wonder if there could be any old palm root down in the ground impeding the magnolia's growth. Surely (if there were any root left) it would be rotted away by now. Hmmmm. Funny thing is...the friend who gave me the tree had two (that he had gotten from the same place). He never planted his and it has more than doubled in height just sitting in it's original pot.

I would try an Azeala, Camillia, Gardenia fertilizer. Magnolias LOVE acid.

I have a magnolia tree doing the exact thing as you are describing. It is blooming every year but has only grown about 3 feet in 6 years. I know when we planted it we spread the roots from the bottom. Also we put mulch around it but it still blooms big white flowers. I just can't figure this out. Any other suggestions

Is it possible that it was planted too deep? There's a guy on a local radio gardening show who says if a tree is planted too deep it will live but not grow bigger. The soil surface should be even with the very top of the first roots that go out from the trunk.

Found this when I was looking for why my magnolia wasn’t growing.... sorry to say, mine has been in 20 years and is maybe 8 feet tall. Blooms every year, nice shiny leaves but the trunks, has 3 trunks, are less than 2 inches in diameter. Plan on trying the 10-10-10 fertilizer.... I just wanted a 15 foot treee there....

All of my Magnolias grew from seeds that I dispersed around the yard. Extreme variation in tree sizes, including some very small after many years. Identical variation among my many Oaks. Perhaps this is a trait of trees in general. Luck of the draw, so to speak.

Transplant shock.

I have had somewhat the same problem. I purchased 2 Little Gems 4 years ago and one grew like 4-6 inches. The other not at all. Soil was tested with 5.7 pH, has full sun light, watered correctly, blooms every year, nice big green leaves, but just will not get taller. Now I do not have mulch around the tree. It is grass and I am seeing people write to have mulch around. I did in fact loosen the root ball as the nursery prescribed. Little gem is a slight over statement. Lol. Really not sure what to do at this point. Any help, ideas or suggestions?

In this thread we have data. Small sample, obviously. It counts. After attention to the minute data (pH, roots, sunlight, etc.), there remains to be considered the macro data point which is height behavior for this cultivar at large. Height distribution across a large population might reveal that the variations described in this thread are not anomalous. And keep in the forefront of the pondering that yours is a cultivar.

No problems with Magnolia grandiflora growing like a week on steroids here in the North (NJ/Zone 7B). Little Gem is a dwarf and I have issues with this one in the ground, growth is too slow, so DEER will rut it ever year, non dwarves can protect themselves. I use 0 weed killer, and don't fertilize.