Tree · Magnoliaceae
Southern Magnolia
Magnolia grandiflora
A grand evergreen of glossy dark green leaves and huge lemon-scented white blooms that hold a landscape for generations.
Full sun
Every 7–14 days
USDA 6–10
60–80 ft · 18.3–24.4 m
Overview
Up close the southern magnolia is a study in contrast. Its leaves are thick and stiff, almost hard to the touch, glossy dark green across the top and, on many trees, lined underneath with a felt the color of rust. The whole broad-leaved evergreen builds to 60 to 80 feet (18 to 24 m) of that heavy, polished foliage. From late spring into summer it opens huge white flowers, each one cup-shaped and lemon-scented, pale and rounded against the dark leaves.
This is a big tree with a big physical presence. The canopy throws dense shade the year round, and the roots run wide and shallow just under the surface, ridging the ground and crowding out grass. All year it lets go of its stiff, leathery leaves, its spent flowers, and its cone-like fruit, which pile up as coarse, slow-rotting litter. That steady fall of heavy debris is the reason to keep it well away from lawns and foundations.
Give it the ground it likes and it mostly fends for itself. The roots want rich, moist, acidic soil and steady water while they take hold, and after that the tree carries on with little help, rarely marked by anything worse than a patch of scale on the twigs. Newer cultivars have carried that same glossy, felt-backed foliage well north of the tree's old range, so colder gardens can grow it now too.
Care
The short version: full sun to part shade, rich and evenly moist acidic soil, deep watering through dry spells while the tree is young, and next to no pruning beyond dead or crossing wood.
Light
Southern magnolia takes its fullest, densest form in full sun, and it still grows in partial sun and partial shade. Under strong light the crown fills in tight and heavy with flowers; in shade the branches spread looser and more open, and you can see straight through the gaps. The leaves keep their glossy dark green either way.
Water
Keep the soil consistently moist, soaking it deeply during dry spells and above all while the young tree roots in. Once established, a deep drink every 7 to 14 days in dry weather holds it steady. It tolerates neither prolonged drought nor standing water, so even moisture is what it wants.
Soil
Set it into rich, organically rich, well-drained loam that stays moist to the touch. The roots run acidic, most at home at a pH of 5.0 to 6.5. They push through clay if they must, but waterlogged or extreme ground sets the tree back.
Temperature
The tree stands up to a wide range, from about -9°F to 100°F (-23°C to 38°C), which spans Zones 6 through 10. Out at the cold northern edge, a hardy cultivar is the surer bet.
Humidity
Plain outdoor air is enough, so there is no level to hit. In warm, muggy weather algal leaf spot can print greenish-gray patches on the leaves, but the marks are only skin deep.
Feeding
Feed once in spring with a balanced or acid-forming slow-release fertilizer made for acid-loving trees. Keep it sparing, since too much nitrogen forces out soft new growth that scale insects settle on.
Pruning
The tree barely needs the saw, so pruning is light work. Cut away dead, damaged, or crossing branches in late winter to early spring. Where the lowest limbs sweep down to brush the ground, you can leave them to curtain over the fallen leaves rather than bare the trunk.
Repotting
A tree in the ground is never repotted, and even a potted one shifts only rarely. On a nursery plant, watch for roots coiling around the rootball, roots poking out the drainage holes, and water sliding straight through instead of soaking in.
Size & spacing
This is a large tree, 60 to 80 feet (18 to 24 m) tall and 30 to 50 feet (9 to 15 m) wide at full size. Leave it that whole open footprint, clear of buildings and lawn, so the broad crown and the shallow surface roots both have somewhere to spread.
When to plant
This is a tree set in place for good, not a crop timed to a season. Plant it in spring or fall while the weather stays mild. From then on the moment to watch for is the bloom, when those big white flowers open across the dark foliage from late spring into summer, thickest in May and June and scattering on more sparsely after.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring or fall
- Harvest: Late spring to summer (May to June, with sparse continued flowering through summer)
Hardiness
USDA hardiness zones: 6–10
Temperature: down to -23°C
Troubleshooting
A healthy southern magnolia shows almost no flaws, and the few it does turn up right on the twigs and the surfaces of the leaves, where the eye catches them. Caught early, most are easy to clear. Match the look of the problem below, then act before it spreads.
Whole branches wilting and browning out one at a time
When separate branches wilt and brown on their own, the usual cause is verticillium wilt, a soil fungus that clogs the wood from within. Cut into the bark and you may find dark streaks running through the vascular tissue, though only a lab test says for sure. Nothing chemical cures it, so cut out the dead wood and hold the tree strong with steady water and feeding.
Fix:
- Prune out and destroy affected dead branches
- Fertilize and water during dry weather to support recovery
- There is no chemical cure; keep the tree vigorous
Waxy white shells on the twigs above a sooty black coating
The raised, shell-like white bumps crusting the twigs are magnolia scale, one of the few pests this tree draws. The insects feed and weep sticky honeydew, and a black sooty mold spreads over it, coating the leaves below in a dull film. Prune out the worst-crusted twigs, smother the overwintering scale with horticultural oil in the dormant season, and treat the crawlers in late summer.
Fix:
- Prune out and destroy heavily infested twigs
- Apply horticultural oil during the dormant season to smother overwintering scale
- Treat crawlers in late summer when young scales are active
Dark spots and blotches freckling the leaves, with some dropping early
Most of the spots freckling the leaves are fungal or bacterial, and warm, humid weather can add the greenish-gray, slightly raised patches of algal leaf spot. None of it cuts deep enough to harm the tree. Rake up and bin the fallen leaves, open the canopy with light pruning to let air slip through, and skip the sprays, which rarely earn their place here.
Fix:
- Rake up and dispose of infected fallen leaves
- Improve air circulation by spacing and selective pruning
- Chemical control is rarely needed
Toxicity
For anyone with animals around, the southern magnolia is safe. The ASPCA lists magnolia as non-toxic to cats, dogs, and horses, and nothing in the tree poisons people, livestock, birds, or rabbits. The worst a big mouthful of those tough leaves might bring is a brief, mild bout of stomach upset, the same as with many plants.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
The ASPCA lists magnolia as non-toxic to cats, so a chewed leaf is harmless. A cat that eats a mouthful of the tough foliage might drool or bring it back up once, the way any coarse leaf can turn a stomach.
Dogs None
Dogs can bite through the leaves with no poisoning risk. The most a big mouthful brings is a short spell of vomiting or loose stool as the fibrous, leathery pieces work through.
Horses None
Horses are clear too, magnolia sitting on the ASPCA non-toxic list. The stiff, leathery leaves make poor browse, and a stray mouthful does no harm.
Rabbits Safe
No toxin in the tree reaches a rabbit. Their gut takes only small amounts of fresh greenery, so an odd leaf is best left a curiosity rather than a meal.
Livestock Safe
Cattle, goats, and sheep can graze beside a southern magnolia safely, since nothing in it is poisonous to them. The hard, stiff evergreen leaves get passed over anyway.
Birds Safe
The tree holds no chemical danger for birds, which tuck into its dense canopy to roost and nest. Some peck at the bright red seeds that show in fall without any harm.
People Safe
Southern magnolia is not poisonous to people, and no part is known to hurt anyone who handles it. The leaves and flowers are not food, though, so there is no reason to eat them.
As with any plant, ingestion of plant material may cause mild, transient gastrointestinal upset even though the plant is non-toxic.
Varieties
Several named selections tweak the look of the wild tree, trading some height for cold tolerance, smaller leaves, or a tighter shape. These are the ones worth a close look.
Little Gem
A compact semi-dwarf topping out near 30 feet, its leaves and flowers scaled down, that starts blooming young and fits a yard too small for the full-size tree.
Bracken's Brown Beauty
A cold-hardy, compact selection good to Zone 6, its smaller leaves backed underneath by a thick felt of deep rusty brown.
Edith Bogue
One of the toughest for a rough site, known for coming through cold, wind, and heavy snow unscathed.
D.D. Blanchard
A vigorous grower rising to about 75 feet on one straight trunk, its leaves dark and mirror-glossy over rich brown undersides.
How to propagate
You can raise a southern magnolia from seed or clone one already growing, though each way asks for patience. The choice comes down to whether a particular cultivar's traits need to carry through.
SeedModerate
Sow cleaned seed in fall or after cold stratification · Several months to germinate; years to reach flowering size
Rub off the red fleshy coat first, then sow the cleaned seed in fall or chill it through a cold spell before sowing. Germination drags on for several months, and the seedling spends years reaching flowering size as it sinks a strong taproot. Seed never copies a named cultivar, so use it only where any outcome is welcome.
Air layeringModerate
Spring to summer on actively growing wood · Several months to root
Air-layering is the surest way to clone a southern magnolia and carry its cultivar traits across. Work on actively growing wood from spring through summer, and let it root over several months before you cut the new plant away.
Stem cuttingsDemanding
Semi-hardwood cuttings in summer · Several weeks to months under mist
Take semi-hardwood cuttings in summer, dip the ends in rooting hormone, and hold them under mist. Roots come slowly and unevenly here, from several weeks to a few months, which is what makes this the trickiest route.
GraftingDemanding
Late winter to spring · One or more seasons to unite
Grafting from late winter into spring binds a named cultivar onto seedling rootstock so the new tree keeps its parent's traits. The join needs one or more seasons to knit solid, and the cut work takes a skilled hand.
Myths
Southern magnolia is poisonous to dogs and cats.
The ASPCA lists magnolia as non-toxic to dogs, cats, and horses, so a pet that bites into a leaf faces no danger. The most that comes of it is a brief, mild stomach upset, the same as any coarse plant material. The tree is safe to grow around pets.