Quercus robur Fastigiata Koster

Quercus robur 'Fastigiata Koster' is one of the best varieties of fastigiate oak to plant in avenues or as a specimen.  This improvement of 'Fastigiata' forms a tree with a more regular and narrower habit, columnar, widening at its base over time to form a pyramid that is both slender and dense. Its marcescent foliage remains attached to the branches until the new leaves appear in spring.  It is less susceptible to powdery mildew than that of other cultivars. Remaining decorative until late in the season, this native tree complements hedgerows beautifully. Its relatively moderate growth is suitable for medium-sized gardens as well as large gardens. It is a very robust and hardy tree that only fears drought and poor, shallow soils. 

The common oak, also known as the English oak, belongs to the family Fagaceae. It is native to a large part of temperate Europe. This species appreciates sub-oceanic to oceanic or more continental climates, which are relatively wet.  It is a very common tree in our plains and low-altitude hills, but rare in Mediterranean regions, which are too dry and hot. In its natural environment, it can reach a height of 50 m (164ft) with a spread of 25 to 30 m (82 to 98ft), while its trunk can measure up to 2 m (7ft) in diameter. In our gardens, it will reach an average height of 27 m (89ft) with a spread of 20 m (66ft). With a relatively exceptional longevity, this oak can live up to 2000 years according to some estimates. Deciduous oaks have the advantage of producing a good and abundant soil, which is favourable for the growth of plants that germinate under their cover.

Quercus robur 'Fastigiata Koster' is a clone of 'Fastigiata' obtained through vegetative propagation. This oak's growth is quite fast. Its habit is initially compactly columnar and then widens at the base to form an erect pyramid 15 m (49ft) tall and 3 m (10ft) wide. The trunk, rather short, is covered with initially green and smooth bark that becomes dark grey, thick, and deeply fissured. The crown is conical and dense. Its young branches are glabrous, reddish-brown, and shiny. The late deciduous foliage consists of alternate, soft, obovate leaves that are larger than those of the species. Each leaf is divided into 5 to 7 pairs of asymmetrical rounded lobes, separated by relatively deep sinuses. The base of the lamina is narrow and has 2 small lobes. The colour of the lamina is a dark bluish-green on the upper side, with the lower surface being paler. The leaves turn reddish-brown, quite late in autumn, and remain attached until spring.  This oak flowers in April-May, shortly after the leaves appear, on the annual shoots.  The male inflorescences are elongated, pendulous catkins, tinted yellow. They are produced on older branches. The female flowers give way to ovoid and elongated acorns, measuring 1.5 to 3 cm (1in) in length. They are often grouped in pairs or threes and attached to a long peduncle. A cupule covered with scales covers one-third of the acorn. The colour changes from green to brown at maturity, in September and October. The root system of this tree is deep and powerful, with both a taproot and widespread lateral roots, providing a solid and durable anchorage in deep and compact soils. 

The 'Fastigiata Koster' oak is an ornamental tree in all seasons, its compact columnar silhouette makes it a versatile garden tree. It can be planted individually or in avenues, in a sufficiently large area to accommodate it. It also provides pleasant shade and a refuge for small wildlife. Its fruits, sometimes produced in abundance, feed small animals such as squirrels and jays. It can be associated, for example, with maples, beeches, limes, and Sophora in a large park.