Quercus variabilis Seeds | Chinese Cork Oak

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Chinese Cork Oak (Quercus variabilis) seed — Chinese Cork Oak (*Quercus variabilis*): Fagaceae — Quercus, native to Broad-leaved forest from the hills around Beijing south through Shaanxi, Gansu, Henan, Hubei and Sichuan to the lower Yangtze and Yunnan, extending into Korea, Japan and Taiwan.

LATIN NAME: Quercus variabilis

COMMON NAME: Chinese Cork Oak

Plant Profile

The leaves are oblong and toothed, and each tooth ends in a fine bristle that stays stiff when the leaf dries: the same feature that tells the Cerris and Lobatae oaks from the rounded-lobed white oaks. The upper surface is a plain dark green. The underside is the giveaway, densely clothed in grey-white hairs that give the canopy a pale cast when the wind turns the leaves over. The leaves colour to a soft gold before they fall and hold late, so the tree keeps some presence into the cold months.

Because it belongs to the Cerris group, the tree flowers in spring and ripens its acorns in the autumn of the following year, so two crops are on the tree at once and the acorn drop is erratic from season to season. The acorn itself is large, and the cup that holds it is covered in long, narrow, recurved scales that give it a shaggy, fringed look. The kernel is starchy but bitter with tannin, and it has been eaten after leaching and used as feed for pigs.

Sawtooth oak carries similar bristle-tipped leaves and is often planted on the same hillsides, so the two get mixed up. Turn a leaf over: Chinese cork oak has a dense grey-white felt underneath, while sawtooth oak is glossy and almost bare beneath. If you can reach the trunk, the answer is easier still, because only this species builds the thick fissured cork layer.

Science & Biotechnology

Rings and logs of this oak are cut as bed logs for cultivated oak mushrooms, and the wood’s density and slow decay suit the purpose well. The bark and acorn cups supply vegetable tannin for leather and for net preservation, and the timber serves for tool handles, mine props and charcoal. As a landscape tree it is planted on poor hillsides for cover and for its tolerance of both summer heat and hard winter cold. The acorn crop feeds jays, wood pigeons and rodents, and the tree is an important host for ectomycorrhizal fungi.

Uses & Benefits

This is the tree that made cork a Chinese industry. Its trunk builds a deep, fissured layer of corky tissue that can be stripped in panels, and stands in Shaanxi, Gansu, Henan and Hubei have been worked for cork, tannin and fuel timber for a long time. Nothing about the tree is harmed by the harvest; the bark is a renewable crop, and the tree grows a new layer underneath the cut. Cork from this species goes into board, insulation, floats and gaskets.

Cork is made by a layer of dividing cells called the phellogen. The first sheet a tree produces is virgin cork: a cracked and irregular layer, useful only for grinding. Once that is removed, the tree forms a new phellogen and lays down a smoother sheet, and it is these later harvests that give the even, workable material. The operation is skilled work with a curved axe: panels are scored to a depth that reaches the phellogen but not the living wood beneath, then levered off whole. Trees are stripped on a long rotation and left to rebuild the layer.

Voles and rabbits will strip the bark of a young oak in a hard winter, so wrap the lower stem in a mesh guard and keep the mulch a little clear of the trunk. Weevils lay in developing acorns, and a proportion of any collection will have a small round exit hole; float the acorns in water and discard the ones that come up light. Oak mildew on the foliage is usually cosmetic and needs no treatment.

Growing from Seed

The seedling makes a long taproot before it makes much top, so use a deep tube or a bottomless pot plunged into the ground. Lift and plant out while the tree is still small enough to move without breaking that root, and choose the final site carefully, because oaks transplant badly once the taproot is established. Keep the ground around the young tree free of grass for the first seasons.

Our Take

Plant the acorn where the tree is to stand, protect it early, and be ready to wait; a cork harvest is a long project, but the tree that produces it will outlive you. Comparisons are useful across the oaks: cork oak is the Mediterranean species that supplies most of the world’s bottle cork, sawtooth oak is its look-alike on the same hillsides, and oriental white oak is the round-lobed relative of the same forests. If you want a faster start in the genus, English oak is the more familiar choice for a parkland tree.

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