Tree · Platanaceae
American Sycamore
Platanus occidentalis
Give it room and moist ground and the American sycamore matures into one of the East's largest shade trees.
Full sun
Every 7–14 days
USDA 4–9
75–100 ft · 22.9–30.5 m
Overview
The American sycamore is a true giant. Native across the eastern United States, it stands among the largest hardwoods on the continent and grows fast, climbing 75 to 100 feet with a crown spread to match. The surest field mark is the bark, which exfoliates in jigsaw plates and exposes a smooth, pale, almost white upper trunk.
Site this tree for open ground, not a tight lot. It performs best in deep, moist, rich soil and takes wet sites, clay, sand, compaction, and even occasional flooding in stride. The cost of that size is litter: large leaves, shedding bark, twigs, and round buttonball seed heads fall throughout the year, and the heavy surface roots will lift pavement and press against a foundation.
Given space, it asks for little upkeep. The chief concern is anthracnose, a spring fungus that browns the emerging leaves during cool, wet weather, though the tree reflushes and suffers no lasting harm.
Care
The short version: full sun and deep, moist, rich soil, with ample room for a tree that clears 75 feet. Water young trees through drought, prune in dormancy, and clear the leaf litter to hold anthracnose down.
Light
Sycamores demand full sun and put on growth fastest in the open, though they tolerate some partial shade. Crowding and deep shade trap still, humid air around the canopy and invite powdery mildew, so give the tree both room and light.
Water
This is a bottomland and streambank tree, so it favors deep, moist ground and even handles wet feet and brief flooding. Dry soil shortens its lifespan, which is why young and establishing trees need watering through any drought. A settled tree on a good site largely supplies its own water from the deep moist soil it roots into.
Soil
Few trees are less particular about soil. It does best in deep, moist, rich earth yet tolerates clay, loam, sand, compaction, and high pH without trouble. The one condition it cannot endure is ground that stays bone dry, since drought cuts its life short.
Temperature
Hardy across USDA zones 4 through 9, the sycamore weathers a broad temperature range, from roughly -29°F to 100°F (-34°C to 38°C). The real cold-season risk is not the tree's hardiness but a cool, wet spring, which is exactly the weather that drives anthracnose into the emerging leaves.
Humidity
Outdoor humidity tracks the weather, and the sycamore handles whatever comes. Airflow matters more than the moisture in the air, because a crowded, shaded canopy holds the still, damp conditions that let powdery mildew and anthracnose establish.
Feeding
A tree in good soil seldom needs feeding. Where the ground is poor, a balanced tree fertilizer in spring keeps a young or struggling sycamore growing strongly, and that vigor is its best defense against disease.
Pruning
Prune in dormancy, removing dead, crossing, or anthracnose-infected twigs. Carry the infected leaves and twigs off and destroy them rather than leaving them beneath the tree, where the overwintering fungus would reinfect the next spring's flush.
Repotting
A sycamore belongs in open ground, not a container, so it is rarely repotted. If you are holding a young one in a nursery pot, move it up before the roots start circling or escaping the bottom and before the top growth stalls against the cramped root space.
Size & spacing
Plan for a giant: this tree reaches 75 to 100 feet tall, or 23 to 30 m, with a spread to match. Keep it well clear of pavement, foundations, and small lots, because the strong surface roots and sheer scale allow no room for second thoughts.
When to plant
The American sycamore goes into the ground while dormant. Set it out in spring or fall during dormancy, watch for the inconspicuous flowers in April, and plan for the round buttonball seed heads to ripen and scatter from fall 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 registers on the leaves, and on an established tree most of it is cosmetic rather than dangerous. Match the symptom below before treating, because a fungicide does nothing against an insect and the reverse holds too. Catch the early signs and your intervention actually counts.
Scorched brown leaf margins that intensify season after season
Scorch that creeps wider and deeper each year points to bacterial leaf scorch (Xylella fastidiosa), a xylem-clogging bacterium moved tree to tree by sap-feeding insects and confirmed only by a lab test. Because the pathogen blocks water flow in the xylem, the symptoms mimic plain drought stress on a tree built for moist ground, so rule out dry soil before you assume the worst. Nothing cures the infection once it is established, but pruning the most affected limbs, irrigating through droughts, and holding the tree's vigor can extend its useful life for years.
Fix:
- Prune infected branches
- Provide irrigation during drought
- Maintain vigor; antibiotic injections may suppress symptoms
New spring foliage browning and collapsing as it opens
The culprit here is sycamore anthracnose, a fungus (Apiognomonia veneta / Discula) that turns active in a cool, wet spring and kills shoots about as quickly as the buds break. The infection runs hardest when leaf-out temperatures sit below 55°F (13°C) for roughly two weeks, because that cool damp window lets the fungus colonize tender tissue before it hardens off; year after year of girdled twigs forces the stubby, congested growth called a witches'-broom. Clear and destroy the fallen leaves and infected twigs to cut off the inoculum, take out the dead wood, and keep the tree watered and fed so it can drive a clean second flush.
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
Powdery white film coating the leaves and young twigs
Those dusty white-to-gray patches are powdery mildew (Erysiphe platani), a fungus that takes hold on crowded, shaded growth where still air and trapped moisture let the spores germinate and spread. It distorts the leaves and pushes them to drop early, yet it troubles a mature tree very little. Thin the canopy so air moves through it, keep the tree growing strongly, and turn to sulfur or horticultural oil only when a young tree carries a heavy infection.
Fix:
- Improve air circulation
- Maintain plant vigor
- Apply myclobutanil, propiconazole, sulfur, or horticultural oil if severe
Pale stippling on the leaf tops with a bronzed tone
Flip a flecked leaf and you'll find the sycamore lace bug (Corythucha ciliata), a small lacy-winged insect that feeds on the underside and drains cell contents, leaving dark fecal spots below and the pale stippling and bronzing above. Alarming as it looks, this feeding rarely sets back a healthy tree. Let natural predators thin the population, rinse light numbers off with a jet of water, and bring in insecticidal soap only when an infestation turns heavy.
Fix:
- Encourage natural predators
- Wash off light infestations with a water spray
- Use insecticidal soap or imidacloprid when necessary
Toxicity
Reassuring news for a household with animals: the American sycamore is non-toxic to cats, dogs, and horses, and nothing about it poisons wildlife or livestock. The single catch is mechanical rather than chemical. The fine hairs shed from spring leaves and buttonballs can irritate 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 classes this tree as non-toxic to cats, so an investigative bite carries no poisoning risk. There is no special precaution to take.
Dogs None
A dog can mouth the leaves or bat a fallen seed ball around with no toxic danger. If one bolts a wad of plant matter, any brief stomach upset clears on its own.
Horses None
Horses sit on the ASPCA non-toxic list for this tree as well, so grazing in its shade raises no poisoning concern.
Rabbits Safe
Neither the leaves nor the bark holds anything poisonous to rabbits. As with any unfamiliar green, offer it in small amounts at first so their digestion adjusts.
Livestock Safe
Cattle, goats, and sheep can browse the foliage safely, since the tree carries no toxic principles.
Birds Safe
Birds nest, perch, and work over the seed heads without harm. The buttonballs serve as a known winter food and present no hazard.
People Safe
The tree poses no poisoning risk to eat or handle. The genuine nuisance is mechanical: fine hairs shed from emerging spring leaves and buttonballs can irritate eyes, skin, and lungs, so put on eye protection and a dust mask when raking or pruning 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 is a single species, but its anthracnose problems steered nurseries toward the London planetree and its more disease-tolerant selections. These are the names you will run into most.
London planetree (Platanus × acerifolia / × hispanica)
A hybrid of American sycamore and Oriental plane, this tree carries far better tolerance of sycamore anthracnose than the native species, which is why it dominates so many street plantings.
'Bloodgood'
Extension sources name this London planetree selection specifically for its resistance to anthracnose.
'Liberty'
This London planetree cultivar is reported to hold off anthracnose and powdery mildew alike.
How to propagate
You can raise a sycamore from seed or from a cutting, and one of those routes is considerably easier 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 straightforward path. Sow in fall once the buttonballs break apart, and skip any pretreatment, because the seed is light-dependent and germinates only with direct light striking the soil surface, so do not bury it. Given that exposure, a seedling can add 3 to 4 feet (90 to 120 cm) in its first 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 succeed only off the right wood. Take hardwood cuttings in late winter during dormancy, or softwood during active growth, and draw them from young, fast-growing stems, because tissue from a mature tree has lost the capacity to root by ordinary means. Allow several weeks for roots to form and a season or more before the young tree is firmly established.
Myths
American sycamore is poisonous to dogs and cats.
The ASPCA lists the tree as safe for cats, dogs, and horses, so a pet that chews a leaf or seed ball faces no poisoning. The irritation it can cause is mechanical, not toxic. The fine hairs shed from spring leaves and buttonballs abrade skin and airways, and that nuisance lands far more on people than on animals.
American sycamore and London planetree are the same tree.
The two share a genus and a strong resemblance, but the London planetree is a hybrid of American sycamore and Oriental plane rather than the native species itself. The hybrid resists sycamore anthracnose far better, which is the chief reason it has largely displaced true sycamore along streets.