Robinia pseudoacacia Altdorf - Black locust

Robinia pseudoacacia 'Altdorf' is a variety of black locust that is rarely cultivated, particularly ornamental in spring. It is a deciduous tree with significant growth that combines yellow foliage, red young shoots, and a generous spring flowering in cream-white. This very fragrant flowering is also loved by bees. With its airy habit and light foliage, this black locust provides dappled shade without harming the plants around it. It is appreciated for its truly accommodating character.

Robinia 'Altdorf' is a cultivar likely selected at the arboretum of Altdorf located in Bavaria, near Nuremberg in Germany. It is derived from Robinia pseudoacacia, a tree native to the eastern U.S.A, belonging to the legume family. In this family, plants can assimilate atmospheric nitrogen at their roots and therefore do not need to draw it from the soil, a characteristic that allows them to thrive in poor conditions.

'Altdorf' is fast-growing, typically reaching 20 m in height and 10 m in spread. This tree forms a trunk that can become very wide, with several distinct ranks of leafy branches. The bark, initially smooth, takes on a rather interesting fissured texture with age. The branches consist of strong yet brittle branches, equipped with a few thorns. The shoots are also armed with thorns grouped in pairs at the base of the leaves. The young shoots are beautifully coloured red in this 'Altdorf' variety. Its deciduous leaves, measuring 15 to 20 cm long, are divided into around twenty leaflets. They transition from spring yellow to summer acid green, before turning yellow in autumn. Flowering occurs in May, on individuals around ten years old. The pendulous inflorescences, measuring 10 to 20 cm long, are produced in abundance. They consist of cream-white butterfly-like flowers encased in a brown-pink calyx. This very fragrant flowering with an orange blossom scent attracts pollinating insects and can be cooked into fritters. It is followed by the formation of flat, reddish pods containing a few rare brown seeds shaped like beans. Note, only the flowers are edible; the rest of the plant is highly toxic.

Robinia 'Altdorf' is suitable for parks and large gardens that are not too exposed to the wind. It can be planted as a specimen tree or in a large informal hedge. You can place it against a backdrop of evergreen bushes or conifers (cypress, thuja, yew, junipers). It can also be associated, in a flowering grove and in poor soil, with other low-maintenance and highly ornamental trees or bushes such as Sophora japonica, Chinese soapberry, honey tree or purple honey locust.