Answer: Dwarf southern magnolias generally grow only 20' tall and wide, which is small for a tree. You can expect the roots to be shallow and extend out one and one-half times the diameter of the canopy. As far as I know, the roots meeting the concrete will stop and explore the soil along the concrete, not grow under it and lift it, providing it is planted at least 15 feet away from the driveway. If it's closer, it may pose a problem as it matures.
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