Southern magnolia

Identification and origin

Magnolia grandiflora belongs to the magnolia family, Magnoliaceae. It is native to the southeastern United States, from North Carolina to Florida and Texas, including South Carolina, Georgia, Alabama, Mississippi, and Louisiana. There it grows on the coastal plains, in bottomlands and moist woods, often as an understory tree. It is the state tree of Mississippi.

It is a large evergreen tree, pyramidal to rounded in shape, that reaches 59–78.5 ft tall with a spread of 29.5–49 ft and a trunk that can exceed 3 ft in diameter. The lower branches often sweep the ground. Growth is slow to medium, 12 in – 2 ft a year, faster when young. It is a long-lived tree.

The stiff, leathery leaves are 5–10 in long: dark green and glossy above, they are pale green underneath or covered with a rusty-brown felt called the indumentum. The creamy white, cup-shaped flowers reach 8–12 in across and are intensely fragrant; their floral parts, in which petals and sepals are fused, are called tepals. The main bloom comes in late spring, followed by scattered flowers through summer. As with other magnolias, beetles do most of the pollinating.

The fruits are fuzzy, rusty, cone-like clusters 3–8 in long made up of many follicles. In fall they open and dangle red-orange seeds on slender threads, eaten by birds and small mammals. The dried cones are used in arrangements.

Seed-grown trees are highly variable: dense or open, narrow or broad, and one can bloom in three years while another takes fifteen to twenty. Hence the value of cultivars: ‘Little Gem’, compact with small leaves, blooms young and over a long season; ‘Bracken’s Brown Beauty’, dense with dark brown leaf undersides, is among the most cold hardy, like ‘Edith Bogue’, with its tight pyramidal shape; ‘Teddy Bear’ and ‘Kay Parris’ stay compact; ‘Alta’ and ‘Hasse’ are narrow and dense, useful as screens.

Light

It grows in full sun or part shade. In full sun it thrives if the soil stays moist or can be irrigated; otherwise, part shade suits it better for the first few years after planting. In the wild it is often an understory tree, but in the garden, in full light, it keeps well-furnished branches down to the ground.

Watering

Water a young tree regularly until its roots are established: check soil moisture at the base and water when it starts to dry, without keeping it soggy. Once established, a magnolia tolerates drought well if it has plenty of soil for its roots to spread, but much less in a restricted space or in poor, dry soil; water it during dry spells in that case. It tolerates occasionally wet soil but not swampy ground or prolonged flooding.

Potting mix

The ideal is rich, porous, well-drained, acidic soil with a pH of 5.5 to 6.5, amended with leaf compost at planting. It tolerates clay, sand, loam, and slightly alkaline pH, but soil that is too alkaline does not suit it. It is highly tolerant of salt spray, which makes it a good coastal tree.

Nothing grows beneath its dense canopy: mulch the ground to protect it from erosion. Fallen leaves can be chopped with a mower and left under the tree to recycle their nutrients.

Temperature

It is grown in USDA zones 6 to 10; the cultivars ‘Bracken’s Brown Beauty’ and ‘Edith Bogue’ are the most cold hardy. Its soft wood is prone to breaking in ice storms. At the other extreme, regions that are too hot and dry do not suit it.

Repotting

This is a tree for the ground, though magnolias can also be grown in containers. Its wide-spreading root system reaches three to four times the width of the canopy: that is why it transplants poorly and why saving a mature tree on a construction site is so difficult.

Plant container-grown trees in early fall; field-grown trees are best planted in late winter or early spring. At planting, make sure no roots circle close to the trunk and cut any circling roots: magnolias are prone to girdling roots. Allow plenty of space.

Pruning

It needs little. Because pruning wounds heal poorly, shape the tree while it is young to avoid large cuts later, and prune after flowering. Remove the few branches that form tight, weak crotches. Lower limbs can be removed to clear the base, but keeping them hides the leaves that drop in spring as new foliage appears. With regular pruning it can be grown as a hedge or espalier; ‘Little Gem’ is especially well suited.

Propagation

The species is propagated by seed, but seedlings are variable and sometimes very slow to bloom. Cultivars are propagated by cuttings or grafting, the only methods that reproduce their traits faithfully.

Common problems

• Yellowing leaves, leaf drop, twig dieback: scale insects, some quite large; treat with horticultural oil in late winter and early summer.
• Leaves mined, then riddled with holes: tulip-poplar weevil.
• Twigs on the ground, neatly cut: twig girdler; pick up and dispose of the twigs.
• Twigs that die back from a small hole: black twig borer; cut 3–4 in below the damage.
• Spotted leaves: fungi, bacteria, or algae, especially in humid climates; rake up affected leaves.
• Dying branches: cankers or verticillium wilt; prune out dead wood.
• Leaf drop in spring: normal, as old leaves fall when new ones emerge.
• Wounded bark: it is thin and easily damaged by mowers and string trimmers.

The same symptom can have several causes: examine twigs, leaf undersides, and growing conditions before acting.

Toxicity

No toxicity has been reported for Southern magnolia. Star magnolia, a species in the same genus, is listed as non-toxic to dogs, cats, and horses. As with any plant, it is best to keep pets and young children from eating leaves or cones.