Tree · Platanaceae
American Sycamore
Platanus occidentalis
Mottled bark peeling back to a smooth white trunk, the American sycamore grows into one of the largest shade trees in the East.
Full sun
Every 7–14 days
USDA 4–9
75–100 ft · 22.9–30.5 m
Overview
The American sycamore is built on a giant scale. A native of the eastern United States, it counts among the largest hardwoods on the continent and climbs fast, reaching 75 to 100 feet with a crown spread as broad. The surest mark is the bark: it sheds in irregular, jigsaw-shaped plates of olive, tan, and gray to bare a smooth, pale, almost ghostly white skin over the upper trunk and limbs.
Look closer and the tree carries its size in every part. The leaves are large and broadly lobed, the spring flowers small and easy to miss, and by autumn the branches hang with round, dangling buttonball seed heads the size of small balls. All of it eventually comes down, with the peeling bark, the big leaves, twigs, and seed balls dropping through the year, while heavy surface roots ridge the ground beneath.
Underneath the flaking plates and the bristly seed balls is a tough, fast tree that wants deep, moist, rich soil and little fuss. The one thing to keep an eye on is anthracnose, a spring fungus that browns and kills the new leaves in cool, wet weather, though the tree pushes a fresh flush and seldom takes lasting harm.
Care
The short version: full sun and deep, moist, rich soil, with wide open room for a tree that climbs past 75 feet. Water young trees through any drought, prune while it sleeps in dormancy, and clear away the fallen leaves so anthracnose has nowhere to overwinter.
Light
Sycamores want full sun and put on the most wood out in the open, though they will accept some partial shade. Shade and crowding only let powdery mildew settle onto the leaves, so give the tree open ground and plenty of light.
Water
This is a tree of stream banks and bottomland, so it leans toward deep, moist ground and takes wet feet and brief floods in stride. Dry soil cuts its years short, which is why young and establishing trees need watering through any drought. A settled tree on good ground mostly looks after itself.
Soil
Few trees are less particular about soil. It does best in deep, moist, rich earth yet puts up with clay, loam, sand, compaction, and high pH without a fuss. The one thing it cannot stand is ground left bone dry.
Temperature
Hardy across USDA zones 4 through 9, the sycamore weathers a broad swing of cold and heat, from roughly -29°F to 100°F (-34°C to 38°C). The real cold-season hazard is not the tree itself but a cool, wet spring that drives anthracnose into the tender new leaves.
Humidity
Outdoor humidity rides on whatever the weather hands over, and the sycamore copes with the whole range. Airflow counts for more than moisture in the air, since a packed, shaded canopy is what lets powdery mildew and anthracnose take hold on the foliage.
Feeding
A tree on good ground hardly ever needs feeding. Where the soil runs poor, a balanced tree fertilizer in spring keeps a young or struggling sycamore growing strong, and that vigor is its surest guard against disease.
Pruning
Prune during dormancy, lifting out the dead, crossing, or anthracnose-struck twigs. Haul the infected leaves and twigs away and destroy them rather than letting them lie under the tree, where the fungus would only seed itself back into next spring's growth.
Repotting
A sycamore is meant for open ground, not a pot, so it is rarely repotted. If you are nursing a young one in a container, pot it up before the roots wind around the bottom or slip out of the drain holes and before the top growth stalls out.
Size & spacing
Plan around a giant: this tree runs 75 to 100 feet tall, or 23 to 30 m, with a crown spreading just as far. Set it well clear of pavement, foundations, and small lots, since the strong surface roots and outright bulk leave no margin for changing your mind later.
When to plant
The American sycamore is set out while it sleeps. Plant it in spring or fall during dormancy, look for the small, inconspicuous flowers in April, and watch the round buttonball seed heads ripen and break apart from fall straight on through the following spring.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring or fall while dormant
- Harvest: Inconspicuous flowers in April; round buttonball seed heads mature and disperse fall through spring
Hardiness
USDA hardiness zones: 4–9
Temperature: down to -34°C
Troubleshooting
Nearly every sycamore complaint shows itself on the leaves, and on an established tree most of it is more blemish than danger. Match the symptom below before you treat, since what stops a fungus does nothing against an insect. Catch the early marks on the foliage and you can step in while it still matters.
Parched brown rims creeping along the leaf edges each year
Dry brown burn creeping in from the leaf margins, with the edges curling upward and the trouble deepening season after season, points to bacterial leaf scorch, a xylem disease moved by sap-feeding insects and confirmed by a lab test. Drought on a tree that craves moist ground scorches the leaves in much the same way, so rule that out before anything else. Nothing cures it once the bacterium is inside, but cutting away the worst limbs, watering through dry stretches, and keeping the tree vigorous can stretch its life by years.
Fix:
- Prune infected branches
- Provide irrigation during drought
- Maintain vigor; antibiotic injections may suppress symptoms
Tender new leaves scorching brown at unfurling
The brown, shriveled new leaves are the work of sycamore anthracnose, a fungus that strikes in a cool, wet spring and blackens the soft shoots almost the instant they break bud. It hits hardest when the air at leaf-out sits below 55°F (13°C) for a couple of weeks, and each round of killed twigs leaves behind a knuckled cluster of stubby growth known as witches'-broom. Gather and burn the fallen leaves and dead twigs, cut the blighted wood back to live tissue, and keep the tree watered and fed so it can throw a clean second set of leaves.
Fix:
- Rake up and destroy fallen leaves and infected twigs
- Prune out blighted twigs and dead wood
- Maintain vigor with proper watering and fertilization
- Apply a labeled fungicide (chlorothalonil, thiophanate-methyl, or copper) on small trees if springs are wet
Grayish-white powder filming the leaf surface and twigs
That chalky gray-white dusting across the leaf surface and the slender new twigs is powdery mildew, a fungus that takes hold on crowded, shaded growth and warps the leaves before they yellow and drop ahead of season. The look is far worse than the harm, and a grown tree shrugs it off. Thin the canopy so air moves through it, keep the tree growing strong, and turn to sulfur or horticultural oil only when a young one is heavily coated.
Fix:
- Improve air circulation
- Maintain plant vigor
- Apply myclobutanil, propiconazole, sulfur, or horticultural oil if severe
Fine yellow specks and a coppery bronze glaze on the leaf tops
Flip over a leaf flecked with yellow above and you'll meet the sycamore lace bug, a small insect with clear, net-veined wings that feeds on the underside and dusts it with dark specks while the top fades to a stippled, bronzed sheen. The mottling startles the eye more than it ever sets back a sound tree. Leave the predators to thin them, blast light numbers off with a jet of water, and bring out insecticidal soap only when the bugs swarm thick.
Fix:
- Encourage natural predators
- Wash off light infestations with a water spray
- Use insecticidal soap or imidacloprid when necessary
Toxicity
Reassuring news for a home with pets: the American sycamore is non-toxic to cats, dogs, and horses, and nothing on it will poison wildlife or livestock. The lone catch is mechanical, not chemical. The fine hairs that shed from the unfurling spring leaves and the buttonballs can rasp at eyes, skin, and lungs, so cover up when you rake or prune at leaf-out.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
The ASPCA files this tree under non-toxic to cats, so a curious nibble at a leaf does no poisoning. Nothing extra is called for here.
Dogs None
A dog can mouth the leaves or bat around a fallen seed ball with nothing toxic to fear. Any small stomach upset from bolting plant bits clears up by itself.
Horses None
Horses come to no harm near this tree, which the ASPCA likewise lists as safe for them. Grazing in its shade raises no poisoning worry.
Rabbits Safe
Neither the leaves nor the bark hold anything poisonous to rabbits. As with any fresh green, offer a little at first so their digestion stays even.
Livestock Safe
Cattle, goats, and sheep may browse the foliage without harm, as the tree carries no toxic principles.
Birds Safe
Birds perch, nest, and pluck at the seed heads in full safety. The buttonballs are a known winter mouthful and hold no threat.
People Safe
Nothing about the tree poisons you to eat or to handle. The single genuine nuisance is mechanical: the fine hairs cast off by emerging spring leaves and the buttonballs can scratch at eyes, skin, and lungs, so put on eye protection and a dust mask when you rake or prune at leaf-out.
Not poisonous, but the fine hairs (trichomes) shed from emerging leaves and from the buttonball seed heads can mechanically irritate the eyes, skin, and respiratory tract of people during spring leaf-out; wear eye protection and a dust mask when raking or pruning at that time.
Varieties
True American sycamore stands as a single species, but its run-ins with anthracnose steered nurseries toward the London planetree and its hardier selections. These are the names you will run into most.
London planetree (Platanus × acerifolia / × hispanica)
Bred from a pairing of American sycamore and Oriental plane, this hybrid stands up to sycamore anthracnose far better than the native, which is why it lines so many city streets.
'Bloodgood'
Extension sources point to this London planetree selection for its resistance to anthracnose.
'Liberty'
A second London planetree cultivar, noted for holding off both anthracnose and powdery mildew.
How to propagate
You can start a sycamore from seed or from a cutting, and one of those routes is far gentler than the other.
SeedEasy
Sow in fall after seed balls disperse · Seedlings can grow 36 to 48 inches the first year under good light
Seed is the simple path. Wait for the buttonballs to crumble apart in fall and sow then, with no pretreatment, since the seed must sit on the soil surface in direct light to sprout at all. Give it that light and a single seedling can stretch 3 to 4 feet (90 to 120 cm) in one season.
Stem cuttingsModerate
Hardwood cuttings in late winter/dormancy; softwood during active growth · Several weeks to root, then one or more seasons to establish
Cuttings root only off the right wood. Cut hardwood pieces in late winter while the tree sleeps, or softwood while it is in active growth, and take them from young, fast-growing stems, because wood from a mature tree will not strike roots by any ordinary method. Count on several weeks for roots to push and a season or more before the young tree truly sits firm.
Myths
The American sycamore is toxic to cats and dogs.
The ASPCA passes the tree as safe for cats, dogs, and horses alike, so a pet mouthing a leaf or a seed ball is not being poisoned. The only real irritation is mechanical, not toxic. The fine hairs that drift off the spring leaves and buttonballs can rasp at skin and airways, and that troubles people far more than it does animals.
American sycamore and London planetree are simply one tree.
The two share a genus and look much alike, but the London planetree is a cross of American sycamore and Oriental plane, not the native species itself. The hybrid shrugs off sycamore anthracnose far better, which is the chief reason it has mostly taken the true sycamore's place along streets.