Quercus suber

Cork oak is deservedly one of the most admired evergreen oaks. Native to the Mediterranean basin (SW Europe and NW Africa), it is the national tree of Portugal which is the largest producer of cork that is obtained from its bark. It is both a long-lived tree and at the same time a very old taxon, as records of its existence on our planet have been preserved from Tertiary fossils.

The cork oak is a medium-fast growing evergreen tree with leathery leaves. They are narrowly oval, bright silvery grey as they emerge and medium green and glossy when mature. The reverse retains a silvery gray indumentum. Older plants produce small, elongated acorns.

It has a highly attractive, deeply fissured, grey-brown, soft bark which forms cork. That is harvested every 10 years or so from trees that have reached 30-40 years of age. The tree itself is not damaged though – the cork keeps on growing after every harvest but don’t do it in ornamental garden, it is not a pretty sight. Mature size of trees cultivated in CE climate is about 10 m in both height and width, while in its natural habitat it can reach twice as much.

The canopy is picturesquely uneven, somewhat rounded, but each tree is unique in shape. The branching is dense enough to make a good-looking tree, but young trees are often pruned in spring to achieve a bushier canopy sooner. With its airy habit, fissured trunk, and similar foliage it strongly resembles olive trees, which is why in colder climates it is often planted as their hardier alternative from an aesthetic point of view because you simply cannot force an oak to produce olives however rare or beautiful it is.

Cork oak is not too picky about soil type provided it is well drained. It can even take less fertile soil. Never plant it in heavy clay and water-logged sites where its roots may rot. Even moisture is needed in the first season after transplanting, then it will do with occasional rain. It loves sun and warmth, never plant it in exposed areas of zone 7. For cultivation in Central European conditions always look for plants with hardened wood which is not prone to frost damage. Pruning is best done in early spring and light trimming is possible in midsummer. Hardiness trialed and proved down to -18 °C (USDA zone 7).

Last update 15-01-2023