The name cork oak implies something about its use by man. The tree bears a bark that can be split, then peeled away, without injuring the tree. This unusual agricultural material is then used to make actual corks for wine bottles and other products. Cork oaks are prized for their bark and grow in cultivated forests throughout Europe and in some areas of the United States. Some cork oaks are very old and have been actively harvested for over 200 years.
The leaves of the cork oak are simple, oval and alternately veined with a wavy, slightly toothed margin. The color is dark green on the surface and the underside is whitish and hairy. The flowers form as catkins, small clusters of innocuous blossoms around 2 to 3 inches long. The fruit is an acorn 1 to 1 1/2 inches long, oblong and brown with a loose cap. The bark is the most unique feature of the plant, growing in thick layers that can be peeled away in large sheets from the trunk of the tree.
The cork tree is an evergreen, keeping its leaves in winter. The tree grows very slowly, adding less than a foot of new growth per year. The bark grows equally slowly and the first harvestable cork, known as virgin cork, is usually not taken until the tree is over 25 years old. The tree will grow in zones 9 or 10 within the United States, preferring the warm, dry climate of southern California.
The tree can reach up to 65 feet tall and can spread to around 40 feet wide. It typically has a short trunk that divides into many large limbs that form an irregularly rounded crown that is fairly dense. The trunk can grow very large and can reach 3 to 4 feet in diameter.
Cork oaks prefer warmer, drier climates, similar to those found in the Mediterranean and North Africa. The plant will tolerate a range of soil conditions, from acid to alkaline. Cork oaks are also very tolerant of drought conditions and heat. Young plants will require irrigation on a regular basis to become established.
The cork oak is grown in large forests in Europe, where sheets of the bark are harvested to create cork stoppers for wine and other products. Each tree can be harvested once every 10 to 12 years. Cork oaks are frequently used to line streets, in median strips and parks. The cork oak is also used as a shade tree and specimen plant in residential landscaping.