I have just bought a Magnolia Genie and going to plant it in the middle of my front lawn which is south west facing would welcome all advice on the preparation of the ground and planting of the tree.
I would make a circle of 1m diameter and remove all grass and weed roots. Then dig the whole area over, adding a bag of manure compost from the garden centre, or blood, fish and bone fertilizer. When done, walk over the area to compact it back down a little, then dig a square hole in the middle, twice as wide and deep as the pot it came in. If the roots are wrapped round and round in the pot, loosen them the best you can without causing damage and then plant the tree so that the base of the trunk is at the same soil level as it was in the pot, backfilling with the soil you dug from the square hole.
However, if you have very alkaline (chalky) soil, be aware that many magnolias don't like that at all, but as this is a dwarf variety, one option would be to grow it in a large pot, where it will be happy for many years as long as you keep up with the water it requires. Use a John Innes #3 loam-based compost if you do that.
A trowel in the hand is worth a thousand lost under a bush.