What Is a Cork Tree?

The cork you pull from the wine bottle at dinnertime tonight will be one of 13 billion bottle stoppers produced annually from the bark of the cork oak (Quercus suber). Although the bulk of the cork industry is located on the Iberian Peninsula, cork oaks also grow in North America in U.S. Department of Agriculture plant hardiness zones 7 to 11. You don't have to harvest the bark to reap the benefits of this large shade tree.

The cork oak can grow to a height of 75 feet, and it opens to a broad canopy. The shiny leaves have a dark green color on the upper surface and are silvery underneath; they remain on the tree throughout the year. The acorns are similar to those of other oak species, consisting of an inch-long seed held loosely in a cap. The seeds are food for birds and small animals; you can also grind them into a powder to thicken stews and make bread, or you can roast them and make a coffee substitute. You must first soak them in water for several weeks to leach out the tannins.

Harvesting the bark of the cork tree is nothing new -- archeologists have discovered cork stoppers, buoys and shoes in sites that date to ancient Egypt. Using only hand tools, workers split and peel the bark, then leave it in the open air for six months to cure. Each tree regenerates its bark within a period of 8 to 10 years -- because it lives for about 150 years, it can yield 12 to 13 harvests. Most of the world's cork oak forests are in Portugal, Spain and North Africa, and the worldwide cork industry employs some 15,000 workers.

Although they aren't native to North America, corks oaks grow here and are especially common in the Western states. They are sensitive to frost and should not be planted in any location where the temperature falls below freezing. They prefer well-drained, dry to moderately dry soil and can tolerate wind, as well as salt spray, which makes them especially suited to coastal environments. They thrive in the light shade at the edge of a woodlot or in the full sun of a solitary placement on a hillside or pasture.

If you want to plant a cork oak, choose a location with plenty of room, because it is a large tree and spreads out to dominate its surroundings, although it does so slowly. Plant seeds in an outdoor seed bed while they are fresh. Protect them from rodents, and transplant them into their permanent locations as soon as possible, because they grow deep taproots. You can store the seeds over the winter if you keep them cool and moist. Your local nursery may stock saplings; if you live in California, you can get saplings from the nursery at the University of California at Davis.