Sorbus randaiensis

The Sorbus randaiensis, also known as Randa Mountain Ash, is a beautiful botanical species native to the high mountains of Taiwan. Still relatively unknown to gardeners, this tree with modest dimensions displays magnificent autumn colours, regardless of the climatic conditions or soil type. Its finely cut foliage, coppery when budding, turns green in summer before a blazing autumn display. After a beautiful white flowering in spring, it produces an abundance of small vermilion fruits that stand out remarkably against the foliage and feed birds throughout winter. Very delicate and sumptuously coloured, this small mountain ash is ideal in both small gardens and large landscape settings.

The Sorbus randaiensis belongs to the rose family. This small tree, which grows in forests at altitudes between 2100 and 4200 m (6890 and 13779ft), is perfectly hardy. Its habit is upright, with a relatively short vertical trunk topped by a semi-open column-shaped crown. With fairly rapid growth, it will reach a height of approximately 5 m (16ft) with a spread of 3 m (10ft) at maturity. The foliage is deciduous, and the pinnate leaves measure 12 to 16 cm (5 to 6in), arranged alternately and composed of numerous lanceolate leaflets with toothed edges. The young shoots are copper-coloured, and the summer foliage is medium green. In autumn, it takes on magnificent hues of yellow, rust, red, and purple. From May to June, a multitude of small white flowers appear in corymbs measuring 8-10 cm (3-4in) in diameter. The flowers, 6-8 mm (1in) in size, consist of 5 petals and 15 to 20 stamens. At the end of summer, they give way to orange fruits that turn vermilion red when ripe and remain decorative until winter. The 1 cm (1in) diameter berries bring joy to birds, particularly thrushes, who love them. The bark of this Sorbus is smooth and light brown-gray in colour, covered with white lenticels on mature trees.

This charming Taiwanese mountain ash, with its moderate growth, is well suited to small gardens as well as larger spaces. Its ornamental qualities make it suitable for a spot near the house, either as a specimen tree or in a mass planting. However, be careful of its fruits, which could stain the terrace! It can also be used in the background of flower beds, alone or mixed with other autumn foliage species such as Prunus, hazelnuts, caramel tree, parrotia, or maples. Tall grasses like Miscanthus, a Rhamnus frangula Asplenifolia, and a few orange Helianthus or chrysanthemums will accompany it late into the season. Mountain ashes have shallow roots, and it is not uncommon to see a mature tree knocked down by a storm. Therefore, avoid placing it too close to buildings and in exposed locations.