Thuringian rowan

Synonyms: half-pinnate rowan, pinnately-incised rowan, S. Hybrida.

Thuringian rowan (Sorbus x thuringiaca Fritch.) – a hybrid of plants from the genus Sorbus. It is a spontaneous hybrid between Sorbus aria and the common rowan (S.aria var. longifolia x S.aucuparia). The hybrid was introduced to commerce in 1907 from the Backhouse nursery, England. It was first described by the Austrian botanist Anton Joseph Kerner in «Sched. fl. exs. austro-hung. no. 2443» in 1896.

It is a deciduous tree 10-15 m in height. It grows slowly. Crown erect, ovoid in shape, dense, becoming spreading and irregular with age. Bark rough, gray in color. Shoots brown, thin, woolly-pubescent.

Leaves 8-12 cm long, ovate-elongated, narrowed toward the apex, blunt at the base, often with 1-2 (3) pairs of free, pinnate or decurrent leaflets along the rachis; on the upper part of the blade they are shallowly and broadly lobed, toward the apex becoming toothed, margin finely and sharply serrate. Many leaves lack free leaflets; all have 10-14 veins; upper surface green, glabrous, underside greenish-gray, pubescent. In autumn yellow to orange-yellow.

Flowers up to 1 cm in diameter, white, arranged in corymb-like grayish-pubescent inflorescences 6-10 cm in diameter. Blooms in May.

Fruits up to 0.8 cm in diameter, nearly spherical, edible, scarlet-red in color.

Cultivars: Sorbus thuringiaca 'Fastigiata' (S. x thuringiaca 'Quercifolia')

Hardiness zone: 4a (-29°C)

Location: light-loving, but can grow in partial shade. Prefers warmth and is tolerant of high temperatures. Poorly tolerant of urban conditions, wind-resistant. Grows on almost all soils, from relatively dry to moist, prefers well-drained, relatively fertile substrates. Sensitive to salinization and prolonged severe drought. Does not tolerate alkaline soils. Optimal soil pH – 6-6.5. Groundwater should be at least 2 m deep.

Planting: planting hole size: 60x60x60 cm. Seedlings should not be planted too deep. The soil mix consists of topsoil, 5 kg of peat compost or humus, potassium fertilizer (100 g) and superphosphate (200 g). Acid soils should be limed. Optimal planting period: autumn – from mid-September to early October, or early spring. Spacing between vigorous trees should be at least 3-4 m, for weak-growing trees 1.5-2 m.

Care: does not require irrigation, but responds well to care. From the 3rd year after planting it is recommended to apply organic fertilizers annually – half a bucket of humus or compost, 20 g of potassium sulfate, 50 g of superphosphate. In May ammonium nitrate can be applied at 15 g per 1 sq. m of the trunk circle.

Pruning: to increase crown strength it is recommended to train the main branches at obtuse angles. Pruning is carried out in early spring before bud swelling. On young trees, shoots are lightly shortened to an outer bud and broken or excess branches are removed. On fruiting rowans it is recommended to remove suckers and perform sanitary pruning. The shaping of fruiting plants depends on the fruiting habit. For cultivars that fruit on last year's growth, branches should be slightly shortened and thinned. With weak growth the tree requires rejuvenation pruning to 2-5 year old wood. For rowans that fruit on various types of formations, shorten the half-skeleton branches, also thin and rejuvenate the spurs. Shoots grow quickly and ripen well by winter.

Diseases and pests: It is little affected by diseases and pests. One of the main pests is the cherry slug sawfly. Since rowan is one of the first to leaf out in the garden, it often becomes a target for aphid infestations, which then spread throughout the garden. To prevent this, it is recommended to spray the rowan with the product «Aktara». During the growing season use the product «Fitoverm»).

Propagation: by grafting

Companion plants: weeping willow, barberry, white dogwood, spirea, mountain pine, spruce, columnar thujas, junipers.

Use: used in urban landscaping, in private gardens, and also cultivated as a fruit plant. Used in solitary plantings and landscape groups, for creating avenues, hedges, and as a specimen on a lawn.