Quercus suber Seeds | Cork Oak
LATIN NAME: Quercus suber
COMMON NAME: Cork Oak, Suber Oak
Plant Profile
Cork oak is the western Mediterranean oak whose bark is stripped for cork and then regrows, a crop taken once a decade for two centuries. It grows in Portugal, Spain, southern France, Italy, Morocco, Algeria and Tunisia, mostly on poor acid soils in areas with dry summers and mild winters, and it forms the open savanna woodland the Portuguese call montado. The tree reaches ten to twenty metres, with a stout trunk, a wide crown and small, leathery, evergreen leaves that are grey beneath and toothed at the margin. Its defining feature is the bark: a thick, spongy, deeply fissured layer of cork that insulates the living tissue beneath from fire and drought. Acorns ripen in autumn and are sweet enough to be eaten by pigs, which is why cork oak country is also pig country. The first cork is cut when the tree is about twenty-five years old, and the best quality comes from the third and later harvests.
Science & Biotechnology
The cork layer is produced by a specialised cambium, the phellogen, which divides outwards and lays down cells whose walls are impregnated with suberin, a waxy polyester of fatty acids and phenolics. Suberin makes the tissue waterproof, buoyant and slow to burn, and it is the reason a cork oak can survive a grass fire that kills its neighbours. Because the phellogen sits in the living bark and is protected by the cork it has already made, the tree can be stripped without being killed, provided the cut is made above the level where the cambium can recover. The species is a poor competitor in shade and depends on open conditions maintained by grazing, cutting and, historically, fire. Its root system is deep and it taps groundwater, which keeps it green through the Mediterranean summer. Cork oak woods are among the most biodiverse habitats in Europe, holding the Iberian lynx, the Spanish imperial eagle and a long list of beetles that live only in old cork oak deadwood.
Uses & Benefits
Wine stoppers take the best cork, and although plastic and screw caps have taken part of that market, natural cork remains the premium closure and the one that keeps the sector alive. Lower grades become insulation board, flooring, gaskets, shoe soles and fishing floats. The bark is harvested by skilled cutters who work with axes and must not wound the inner bark; a badly cut tree can take a decade to recover or die. Acorns feed the black Iberian pigs that produce jamón, and the open woods are grazed by cattle and sheep as well. The wood is hard and is used for charcoal and small turnery, though the tree is rarely felled for timber. In gardens cork oak is a handsome evergreen shade tree for a dry, mild climate, and it is used in streets and parks in California and Australia, where it has occasionally naturalised.
Growing from Seed
Sow acorns in autumn, fresh, in deep pots of sandy loam; they germinate in six to ten weeks without pretreatment, though a month of cold improves uniformity. The taproot is long and brittle, so sow in a deep tube and plant out while the seedling is small. Choose a sunny site with well-drained, preferably acid soil, and avoid anywhere that floods in winter. Water for the first two summers, then only in extreme drought; the tree is hardy to about minus ten once established. Protection from rabbits is essential in the first years, since they ring the stem. Growth is slow for the first decade and then speeds up, and the tree can be left unpruned, though a single clear trunk is worth establishing early. Cork production is a matter of decades, not years, so plant it for the next owner.
Our Take
An evergreen oak that makes its own fireproof jacket and pays the rent once a decade. Slow, drought-proof, and worth planting for the long view.
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