All have shallow root systems, so the surrounding soil shouldn't be cultivated too much; underplant with perennials or groundcovers rather than annuals. Magnolias should be bought as balled-and-burlapped or container-grown plants: they have a fleshy root system that breaks easily if you try to plant them bare-root and, unless they're in active growth, the damaged roots will rot rather than heal. It's also preferable to buy small plants since they suffer less root damage.
In most of Canada, spring planting is best, although fall is feasible in regions that have milder winters, such as coastal British Columbia or southern Ontario. Prepare a hole at least twice the size of the root ball so roots can stretch out; site the plant no deeper than it was in its original container. Refill the hole with the original soil, water well and apply a five-centimetre layer of mulch to help retain moisture. Be prepared to water during any prolonged periods of drought during the first year. This is critical to a magnolia's survival (water if leaves feel limp to the touch).
Once established, magnolias may need occasional pruning to keep them in bounds. This should be done in early summer after flowering. Remove damaged and crossed branches, shoots growing toward the centre of the plant and, once the magnolia grows larger, any lower branches that have become an obstruction.
In the wild, magnolias grow in woodlands where they benefit from decomposing leaves. To compensate for this in the garden, feed them with a granular, slow-release fertilizer, such as a 10-10-10 formulation, in early spring. Apply around the plant's drip line, using 250 to 500 grams of fertilizer per 2.5 centimetres of trunk diameter, measured at chest height. For a multi-stemmed tree, add up the diameters of the various stems to determine the amount of fertilizer you need. However, don't fertilize at all for the first couple of years; you want the plant to develop a spreading root system.
While magnolias grown in the Deep South are subject to several fungal problems, the ones grown in Canada are relatively disease-free. Common pests such as slugs and aphids may cause some damage, but it's seldom serious, except on young plants.