Magnolia trees belong to the Magnoliaceae family, one of the oldest groups of flowering plants. They are trees or shrubs that can grow up to 90 feet tall, often with very large white, pink, red, purple or yellow flowers. The flowers and sometimes the bark are sweetly scented. Among the best known species are southern magnolia (Magnolia grandiflora), Loebner magnolia (Magnolia loebneri); saucer magnolia (Magnolia x soulangiana) and star magnolia (Magnolia stellata). To decide how far to plant a magnolia from a house, first determine how large it will be at maturity.
When determining where to plant, the most important considerations are the height and crown width of the mature tree. The root area of a tree is roughly the same diameter as its mature crown, so proper siting means that roots are less likely to penetrate foundations. Magnolias also should be located in full sun and away from the shadow of structural overhangs.
A large southern magnolia tree can reach 60 to 80 feet in height with a spread or crown width of 30 to 50 feet. The bigleaf magnolia is 40 to 60 feet tall with a spread of up to 40 feet. For the best results with these large magnolias, young trees should be planted at a distance from the house equivalent to one-half the width of the mature crown. In the case of the southern magnolia, for example, the safest planting distance would be between 15 and 25 feet from the house.
For smaller spaces, star magnolia, which grows 15 to 20 feet tall, is an excellent choice and can be planted 8 to 10 feet from a structure. The flowers have slender petals and bloom in shades of white or pink. The lily magnolia (Magnolia liliiflora) is even smaller, reaching 8 to 12 feet in height. This means that it can be planted 4 to 6 feet from the house and even can be grown in a pot and moved around.
Fill the Void
It is tempting to plant young trees too close to houses. If you create enough space for the mature crown and roots, there will be a bare spot in the landscape until the tree matures. To fill this, use potted shrubs or perennials or combinations of annuals. As the tree grows, the area shaded by its crown also will grow, making it necessary to change the mix of plants growing in the area from sun lovers to those that thrive in shade.