Chinese chestnut: size, growth rate, bark, and how it differs from the American chestnut

Ask for a chestnut tree at most nurseries east of the Mississippi and what you get is a Chinese chestnut, Castanea mollissima. It is the tree that took over the job when the American chestnut died out, and it does that job well: sweet nuts within a few years of planting, on a tree that shrugs off the blight. It is not the same tree, though, and the differences matter if you are choosing one for a yard, a nut orchard or a woodlot. Here is what it is, how big it grows, how fast, and how to tell it from its American cousin.

Where it comes from, and why it is here

Chinese chestnut is native to the hills of China and Korea, where it has been grown for its nuts for thousands of years. It reached North America in the nineteenth century as a curiosity and a crop tree, and became important only after 1904, when a fungus that had come in on Asian nursery stock was found killing chestnuts in the Bronx. That fungus, chestnut blight, spread through the eastern forest in forty years and killed several billion American chestnuts, a tree that had been one in four of the canopy in parts of the Appalachians.

The Chinese tree had grown up with the blight and carries real resistance. It gets cankers, but it walls them off and grows on, where an American chestnut is girdled and dies back to the roots. That resistance is why nearly every chestnut tree planted in the East since the 1930s has been Chinese, and why every serious attempt to restore the American tree, from the backcross breeding of The American Chestnut Foundation to the transgenic lines now being tested, has been an attempt to move that resistance into an American tree.

How big it gets

A mature Chinese chestnut is a broad tree, not a tall one: 40 to 60 feet high and often as wide, with a short trunk that forks low into heavy, spreading limbs and a rounded crown. Give it 30 feet from a house and from its neighbor, and expect it to shade a circle 40 feet across in the end. In an orchard, trees go 30 to 40 feet apart.

That shape is the first thing that separates it from the American chestnut, which in a forest was a tall, straight-trunked timber tree of 80 to 100 feet and more, with the first limbs far overhead. Open-grown American chestnuts spread too, but even in the open they carried a taller, more upright crown than the Chinese tree ever makes.

How fast it grows

On a deep, well-drained soil in full sun a young Chinese chestnut puts on a foot or two a year, sometimes more, and reaches 20 feet in about ten years. Growth slows as the crown broadens, and a 40-foot tree is a matter of decades, not of a lifetime. Seedlings bear their first nuts at four to seven years, grafted trees at two or three, and a tree in full bearing at 15 to 20 years can drop 50 to 100 pounds of nuts.

For comparison, American chestnut was one of the fastest hardwoods of the eastern forest, and a stump sprout can still shoot up ten feet in a few seasons before the blight finds it. Our own Allegheny chinquapin, the small native chestnut, is slower and smaller but bears earlier still.

Bark, twigs and buds

Bark is the thing people search for and the least reliable way to tell the two apart, because both change with age. A young Chinese chestnut has smooth grey-brown bark that develops shallow furrows and flat ridges as it ages; an old tree is grey and coarsely furrowed, with ridges that tend to run straight or interlace loosely. Old American chestnuts had dark brown bark broken into broad, flat-topped ridges by deep fissures that often spiraled up the trunk, which is one reason old photographs of them look the way they do.

The twigs and buds are far better. Chinese chestnut twigs are tan to buff and covered in short hairs you can see with a hand lens and feel with a fingertip; the buds are rounded and hairy. American chestnut twigs are smooth, hairless and reddish brown, with pointed, smooth buds. If you have a doubtful tree, this is the test.

Leaves and nuts

Chinese chestnut leaves are oval to oblong, glossy dark green above and paler and slightly hairy below, with a rounded or heart-shaped base and short, evenly spaced teeth. American chestnut leaves are longer and narrower, shaped like a canoe, thin and papery, hairless below, with a wedge-shaped base and long, curved, hooked teeth. Chinese leaves also tend to be thicker and to hang more stiffly.

The nuts sit in the same spiny bur, usually two or three to a bur, and drop in September and October when the burs split on the tree. Chinese nuts are the bigger ones, three quarters of an inch to an inch and a half across, with a fine fuzz at the tip and a broad pale scar at the base; American nuts are half that size and sweeter to most tastes, with a much fuzzier tip. Both are eaten fresh, roasted or dried, and both are a heavy fall crop for deer, turkeys, squirrels and bears. If you would rather have the tree identified for certain, The American Chestnut Foundation will identify a leaf and twig sample.

Flowers and pollination

Both chestnuts flower in June, weeks after the leaves are out, with long cream-colored catkins that carry a heavy, sweet, faintly rank scent for a hundred yards downwind. The male flowers are on the catkins; the female flowers, which become the burs, sit at the base of a few of them. A Chinese chestnut is effectively self-sterile, so one tree alone makes empty burs. Plant two seedlings, or a seedling within a hundred feet of another chestnut, and both bear. Seedlings from the same batch are different enough to pollinate each other.

Where it grows, and where it fails

Chinese chestnut is hardy in zones 4 through 8. It wants full sun and a well-drained, slightly acid soil, sandy loam being ideal, and it will take a dry hillside once established. What it will not take is wet feet: on heavy clay that stays wet in spring, or at the bottom of a slope, it is prone to the root rot that killed American chestnuts across the South even before the blight arrived. It is also unhappy on limestone soils, where the leaves yellow. In short, plant it where you would plant an oak of the dry ridges, not a swamp white oak.

Planting and care

Plant bare-root saplings while dormant, from leaf fall until the buds swell, in a hole twice the width of the roots and no deeper, with the root flare at grade and the same soil back in. Nuts can be sown too: they must never dry out, so sow them in fall an inch deep under hardware cloth to keep squirrels off, or keep them cold and moist over winter and sow in spring. They sprout a taproot first and a shoot a few weeks later.

Water once a week through the first summer and in dry spells for two more. Deer browse the leaves and eat the nuts, and voles girdle the young bark, so protect the tree from the day it goes in. Prune only in the dormant season, to a single leader for the first few years, then leave it alone; it makes its own shape. Two pests are worth knowing. Chestnut weevils lay eggs in the nuts, and the cure is to gather nuts every day and get them cold. The Asian chestnut gall wasp, which arrived in Georgia in the 1970s, makes green galls on the twigs and cuts the crop in bad years; parasitic wasps that followed it have brought it down in many places.

What we sell it for

We grow Chinese chestnut for food, not for restoration. It is not native, and it will never be the tree the American chestnut was in the forest. But until blight-resistant American chestnuts are available in numbers, a pair of Chinese chestnuts is the reliable way to have chestnuts in the yard in five years, and a fine wildlife tree besides. Our seedlings are grown from seed, so every one is different and any two will pollinate each other; we also sell the nuts to sow. For the native chestnut of the East, see the Allegheny chinquapin, and for an oak that likes the same dry, sunny ground, the chinquapin oaks and post oaks.

Sources

• The American Chestnut Foundation: The blight, the breeding programs, and where restoration stands.
• Identifying a chestnut: The American Chestnut Foundation: how to tell Chinese, American and hybrid trees apart, and how to send a sample.
• Castanea mollissima, PLANTS Database: USDA: the species profile and where it has naturalized.
• Castanea dentata, PLANTS Database: USDA: the American chestnut’s native range.