Caragana arborescens (tree-like caragana)

Synonyms: yellow acacia, peashrub, Aspalathus arborescens Amman, Caragana inermis Moench, Caragana sibirica Medik., Robinia altagana Pall., Robinia caragana L., black caragana, Siberian caragana, boua

Caragana arborescens (Caragana arborescens Lam.) – the typical species of deciduous shrubs from the family Caragana (Caragana). It was first described in the book «Encyclopedie Methodique. Botanique ... Paris» by the French naturalist Jean-Baptiste Lamarck in 1785. In cultivation since 1752.

Photo: I. Bobyr

Grows in the forest zones of Siberia (Altai Krai, the Sayan Mountains), on the Southern Urals, in Kazakhstan (eastern and central regions), in Georgia, Mongolia. Occurs in the understory of sparse pine and larch forests, on forest edges, ravines and rocky slopes, and in park plantings. Ascends to 1650 m above sea level.

Photo: D. Oreshkin

It is a deciduous shrub, less often a small tree 4–7 m tall. In the first 3 years it grows rapidly, reaching 3.2 m in height at 10 years, with a crown diameter of 2 m. Stem thickness 10–15 cm, with smooth, shiny, greenish-brown bark. Young shoots are covered with greenish or yellow-greenish bark, are angled, appressed-hairy. Buds are ovate-conical, 5–10 mm long, dry-membranous, scales light-reddish or grayish-brown, deeply seated in the axils of leaf cushions. Leaf scar large, with 2 brittle often deciduous spines on the sides. Pith rounded or slightly angled. Wood greenish-brown, heartwood brown. Stipules are awl-shaped, sharp, deciduous or transformed into a thorn up to 1 cm long.

Photo: V. Sviridenko

Leaves alternate, pinnate, consisting of 5–8 pairs of opposite leaflets. Leaflets entire-margined, obovate or oblong-elliptic, 8–35 mm long and 5–13 mm wide, rounded at both ends, with a short point at the apex, initially hairy, later almost glabrous. Petioles deciduous, thin, up to 9 mm long, pubescent, more rarely glabrous.

Photo: V. Sviridenko Photo: V. Solodukhin

Flowers large, bisexual, papilionaceous, solitary or in clusters of 2–5 (4). Pedicels 2–6 cm long, pubescent, arranged in clusters of 2–5, jointed in the upper part. Calyx bell-shaped, up to 6 mm long, pubescent, with short and broad teeth, 6 times shorter than the tube. Corolla yellow, 17–19 mm long; the standard blade broadly obovate, suddenly narrowed into a short claw; the wing blades narrowed in the upper part, the claw 1.5 times shorter than the blade, the ear 3 times shorter than the claw, the keel blunt, with a claw slightly shorter than the blade. Stamens 10, 9 of which are fused into a tube, 1 free. Ovary pubescent or glabrous. Nectariferous tissue at the base of the corolla. Pollen pale orange. Flowers in May–June.

Photo: V. Ivanov

Fruits are legumes linear-cylindrical, 3–6 cm long and 3.5–5 mm wide, blackening, valves twist, containing 3–5 (8) seeds. Seeds brown, glossy. Ripen in July–August. Number of seeds per 1 kg – 40,000 pcs. Begins to bear fruit from 2 years of age.

Photo: N. Degterev

Forms:

• Caragana arborescens f. lorbergii Koehne
• Caragana arborescens var. pendula Carrière
• Caragana arborescens var. redowskii Bean
• Caragana fruticosa (Pall.) Besser
• Caragana fruticosa var. multiflora H.Xie & Y.T.Zhao
• Caragana inermis Moench
• Caragana sibirica Medik.
• Robinia altagana var. fruticosa Pall.
• Robinia mongolica Sw. ex Bess.
• Robinia speciosa Sw. ex Bess.

Cultivars: ’Anny’s’ Golden Cascade’, ‘Nana’, ‘Spring Gold’ (‘Yellow Tip’), ’Sutherland’, ’Tidy’, 'Albescens', 'Walker'.

Hardiness zone: 3f (-45°C)

Site: sun-loving, but can grow in partial shade. Undemanding to soil and moisture, but prefers fresh, slightly acidic or neutral, loamy or sandy loam soils. Tolerates any salinity and compaction of the soil, as well as prolonged drought. Minimum groundwater level 1.5 m, does not tolerate waterlogging.

Planting: for creating a single-row hedge the recommended spacing between plants is 50 x 50 cm, in a double row 70 x 50 cm. Planting depth 50 cm, slight burial of the root collar by 1–2 cm is permissible. Planting is best done in spring or autumn. On heavy soils drainage of crushed stone or gravel 20–25 cm thick is necessary. When planting, 150–200 g of mineral fertilizer can be added. Watering is mandatory – 10–15 L per plant.

Care: in young plantings shallow cultivation and mulching with peat to a layer of up to 5 cm is recommended.

Pruning: tolerates trimming well. For creating hedges shoots are cut back by 1/3–1/2 of their length. For standard (single-stem) forms cleaning of the trunk is required.

Propagation: propagated by seed and vegetatively. Seeds are best sown immediately after ripening in a cold frame. They germinate in the 2nd week. If seeds are stored before sowing, they should be soaked for 24 hours in warm water and sown in a cold frame. In this case, seeds germinate within 2–3 weeks at 20°C. Seed viability 90–100%. Semi-hardwood cuttings, cut 7–10 cm long, are planted in July–August. Produces abundant root suckers. Ornamental forms are propagated by grafting.

Diseases: rust (use 3–5% Bordeaux mixture). Nitrogen-fixing bacteria live in symbiosis on the roots.

Pests: acacia aphid, acacia psyllid, acacia false scale (use 0.4% rotor solution). Jewel beetles, clearwing moths, longhorn beetles (use phthalophos at 1% concentration).

Uses: used in solitary and group plantings. Applied in urban and settlement landscaping, in shelterbelts, for stabilization of mobile soils. Good honey plant (yields up to 40–60 kg of honey over the entire flowering period). Fruits and seeds are used in cooking. Wood is used for various crafts. Leaves and seeds are used for dyeing fabric chestnut and dirty-green colors.