With their large, bold blossoms so proudly displayed, magnolias are undoubtedly the most glamorous and effective of all shrubs or small trees and there is room for at least one specimen in every garden. The polluted air of industrial towns does not worry them in the least, and they are tolerant of a wide range of soils, although some are calcifuge.
April is the best month of the whole year for planting and establishing magnolias. They have fleshy roots which are apt to rot away in winter, following an autumn disturbance. But in spring they can quickly make good any damage done to them, but do remember to keep your young plants well watered until they are thoroughly settled in. The other point to remember about these fleshy roots is that they strongly resent being dug around. You can easily kill a large and mature specimen by digging over the ground near it. Feed, then, entirely with surface mulches of organic material like garden compost, and forebear prodding about with a fork. One reason for magnolias making such excellent lawn specimens is that they are automatically undisturbed there. It would be as well, however, at least in the early years, to keep a circle 5 feet across round your magnolias free from turf, and you could plant small bulbs and hardy cyclamen here.
Christopher Lloyd, The Well-Tempered Garden