Sorbus belongs to the rose family, Rosaceae. It has over 100 species. The species are also known as Whitebeam, Rowan (Mountain Ash), and Service tree.
Found widely in the temperate regions, the species Sorbus Aucuparia (Mountain Ash) is the most popular variety used for bonsai. The other Mountain Ash varieties are:
- Sorbus Cashmiriana, grown as large, spreading shrub or a small tree. It has pink flowers and white fruits.
- Sorbus Commixta ‘Embley’, an upright tree of medium height. It has creamy white flowers and deep red fruits. The leaves turn bright red and orange in autumn.
- Sorbus ‘Eastern Promise’, a small, round tree. It has small white flowers and rose-pink berries. The leaves turn purple and orange-red in autumn.
- Sorbus ‘Joseph Rock’ is an upright tree. It has white flowers and yellow berries. The leaves turn to orange, purple, and red in autumn.
- Sorbus Reducta, a suckering shrub has white flowers and pale pink to white fruits. During autumn, the leaves turn purple.
- Sorbus Sargentiana is a spreading tree of medium size. It has white flowers and red berries. The leaves turn orange-red in autumn.
Few other species that would be equally suitable for bonsai are the Sorbus Alnifolia (Korean Mountain Ash), Sorbus Americana (American Mountain Ash), and Sorbus Cashmiriana.
Sorbus Aucuparia is commonly called Rowan and Mountain Ash. Some other names for it are Amur Mountain Ash, European Mountain Ash, Quick Beam, Quickbeam, or Rowan-Berry. Native to most of Europe, parts of Asia, and Northern Africa, it is often found in woodlands, hills, and mountains. It is an undemanding and frost-hardy plant. One of the shortest-lived trees in the temperate climate, the Sorbus Aucuparia rarely lives for more than 80 years.
The name Sorbus Aucuparia comes from the Latin words Sorbus and Aucuparia. Sorbus means ‘service tree’. Aucuparia is derived from the words Avis meaning ‘bird’ and Capere meaning ‘catching’. It refers to the use of the fruit of Sorbus Aucuparia as bait for bird-catching.
Reaching up to a height of 15 m (49.21 ft), the Sorbus Aucuparia has a slender and conical trunk reaching up to a diameter of 40 cm (1.31 ft). When young, its bark is yellow and gray, and shiny. As it matures, the bark becomes gray and black with vertical cracks. Often having multiple trunks, the crown is either loose and round or irregular shaped and wide.
The leaves are pinnate with up to 12 small leaflets distributed on a main vein and a terminal leaf. They are oblong-lance shaped, 20 cm (0.65 ft) in length, and 8 to 12 cm (0.26 to 0.39 ft) in width. The upper side is dark green while the underside is grayish-green. In autumn, the leaves turn yellow or dark red. When grown as a bonsai, the leaves can be reduced to 2 or 3 leaflets. The roots are wide and deep, and the Sorbus Aucuparia is capable of root sprouting. It can also regenerate after coppicing.
The flowers are small, yellowish-white, and blossoms from May to June in dense clusters. They have five small, yellowish-green, triangular sepals. The lower stalks are longer making the head of the flowers appear flat or slightly convex. The fruits are small, red pomes, ripening from August to October, and eaten by a variety of birds.
The fruits and foliage of Sorbus Aucuparia have been used to create dishes, beverages, traditional medicines, and fodder for livestock. Its wood, tough and flexible, has been used for woodworking. The tree is also used as an ornamental tree.
How long does it take to grow Sorbus Bonsai?
Sorbus Aucuparia can grow in open and sunny areas or partial shade. It can tolerate drought and severe cold. For fast growth, it should be provided with an ample amount of sunlight throughout the day.
Before discussing how you can plant and grow your Sorbus Aucuparia bonsai, let us go through the best conditions and requirements needed for the Sorbus Aucuparia bonsai tree care.
Position and lighting
Sorbus Aucuparia bonsai is not fussy about its position. It grows in full sunlight as well as partial shade. If below -10 °C (14 °F), it will require frost protection. It grows in windy spots, too. On warm windy days, water the Sorbus Aucuparia bonsai 2 to 3 times a day.
Sorbus Aucuparia bonsai is suitable in USDA zones 3a to 7b. It is frost-hardy and can tolerate winter dryness. It can also resist air pollution, wind, and snow pressure. Sorbus Aucuparia bonsai must be protected from extreme temperatures.
Sorbus Aucuparia bonsai tree prefers fertile and well-drained soil. It grows in different soil conditions. It thrives in soil enriched with organic matter and retains lots of moisture during spring and summer. The root system is shallow needing acid to alkaline soil, with some moisture. It will not tolerate the roots to dry out. Sorbus Aucuparia bonsai cannot tolerate saline soil or waterlog. The soil pH should be neutral.
Sorbus Aucuparia bonsai tree must be watered well in its growing season. During the first few months after planting, it will require adequate moisture. In winter, it should be watered sparingly. During summers, regular watering is essential. It helps in keeping the soil cool and provides the tree with sufficient moisture to maintain its vigor. A layer of mulch under the tree keeps the moisture of the soil from evaporating.
You can feed your Sorbus Aucuparia bonsai a general granular plant food in spring. During the growth phase, feed twice weekly. Feeding a low nitrogen bonsai feed, monthly will reduce the size of leaf and leaflet.
Sorbus Aucuparia bonsai tree can be styled in all forms except the formal upright and broom style.
How to plant and grow Sorbus Bonsai
Sorbus Aucuparia bonsai is a hard-working tree. It is mostly grown from seeds.
Sorbus Aucuparia bonsai is propagated from seeds and cuttings. For a bonsai, the seeds should be sown in autumn, and cuttings in early summer. Mix the seeds with equal parts horticultural sand and leafmould or peat-free compost. Layer the bottom of the pot with stones and cover them with sand. Place the seed and sand mixture on top and again, cover it with 2 to 3 cm (0.065 to 0.098 ft) of sand. The pot must be kept outside in winter. If it shows signs of drying, water the pot.
Pruning and wiring
Sorbus Aucuparia bonsai trees do not need much maintenance. Remove the dead or diseased parts and thin out the over-crowded, rubbing branches from time to time. However, if pruning is required, the best time to do it is from late autumn to early spring. The branches must always be removed back to a strong lateral growth whenever pruning a Sorbus Aucuparia bonsai tree. Prune the branches in winter. The new shoots must be trimmed continually during summer to maintain the desired shape. The leaf size can be reduced by removing the leaflets. To encourage branching, Sorbus Aucuparia bonsai tree must be pruned hard at midsummer. The matured trees must be pruned hard in spring. Care should be taken to remove most of the first sets of leaves to keep them small in size.
Repotting a Sorbus Aucuparia bonsai tree must be done every 1 or 2 years. The buds extend during spring. Use a basic soil mix with a layer of organic matter such as compost or well-rotted manure. The bottom of the pot should have a layer of gravel to improve drainage. Requisite drainage is very critical for the roots to develop. Sorbus Aucuparia bonsai is preferably grown during autumn, winter, or spring.
How to care for your Sorbus Bonsai
The Sorbus Aucuparia bonsai is a low-maintenance tree. It does not need much care and attention once it gets established.
Pests and diseases
Sorbus Aucuparia bonsai is infected by a variety of pests and diseases. The pests include aphids, red spider mites, and scale insects. The contagious disease fire blight often destroys the plant. By spraying a good insecticide, you can get rid of the pests. Found in most members of the rose family, fire blight is a destructive bacterial disease. It enters through the tips of the branches and travels down the stems causing dieback. The infected leaves and branch tips turn brown or black, and the bark develops reddish water-soaked lesions. You can see an orange-brown liquid oozing from the lesions on warm days. There is no cure for fire blight. The best remedy to fight it is pruning and removing the infected stems and branches regularly.
The bright orange berries of the Sorbus Aucuparia bonsai tree stand out strikingly against the green foliage before the foliage turns a warm red in autumn. In spring, the tree is decorated with clusters of pretty white flowers. The Sorbus Aucuparia bonsai tree is a fabulous-looking tree that is loved by bonsai enthusiasts.