Broom

Synonyms: Sarothamnus Wimm., Spartocytisus Webb & Berthel., Aulonix Raf., Chamaecytisus Link Handb. Corothamnus (W.D.J.Koch) C.Presl, Diaxulon Raf., Nubigena Raf., Цитиус

Broom (Cytisus) — a genus of deciduous plants in the family Fabaceae (Leguminosae). The genus was first described by the French botanist René Desfontaines in the book «Flora Atlantica» in 1798 . According to one version, the genus name derives from the Greek 'kytisos' — the name of a leguminous plant. According to another version, it comes from the name of the Greek island «Kythinos», where the plant was first found. Cultivated since the early 18th century.

Cytisus supranubius. Photo A. Kovalchuk. Spain, Canary Islands.

In nature it grows in Europe, North Africa and Western Asia. It is found on light sandy and sandy-loam soils or on limestone outcrops.

Members of the genus are mainly shrubs, less often small trees, with deciduous, more rarely evergreen leaves. Shoots are green, glabrous, less often armed with spines. Branches numerous, thin, erect and spreading, prostrate and sprawling, often ribbed or pressed and silky-pubescent with fine hairs. Long-lived, slow-growing.

Cytisus villosus. Photo Xemenendura. Spain

Wood diffuse-porous or ring-porous, with a clearly visible pattern. Heartwood reddish-brown, often diffuse in outline. Sapwood yellowish-brown. Differences in the structure of the wood of different species are insignificant.

Leaves alternate, trifoliate, more rarely reduced to a single leaflet, simple, petiolate. Stipules small or absent.

Cytisus villosus. Photo G. Soltani. Sochi.

Flowers 2-3 cm long, papilionaceous, yellow, white, more rarely purple or pink, axillary, borne in racemes or heads at the ends of shoots. Standard (banner) 0.8-3 cm long, considerably longer than the wings and the keel. Wings folded-wrinkled along the upper edge. Keel with a blunt keel, pubescent. Calyx tubular, less often campanulate or funnel-shaped, bilabiate, 10-15 mm long. The upper lip of the calyx is two-lobed or two-toothed, the lower — with 3 shorter lobes. Stamens 10, fused into a tube. Ovary sessile, less often on a stalk. Style curved, with an oblique, more often capitate stigma. Blooms abundantly and for a long time, in spring and summer, for 30-35 days. The flower has an unusual mechanism. As soon as an insect lands on the flower, the stamens, curved and held under tension by the petal cover, straighten and strike the bee, covering it with pollen. Flowers and fruits begin in the third year.

Cytisus sessilifolius. Photo V. Papchenkov. Spain, Catalonia, Barcelona.

Fruits are flat, broadly linear and densely pubescent pods, two- or multi-seeded, dehiscent at maturity. Seeds reniform, shiny, flat, with an aril.

All parts of the plant contain poisonous substances.

Species: the genus includes about 63 species. Of these, only 32 species (including 5 hybrids) are used in ornamental horticulture.

· Austrian broom — Cytisus austriacus L.
· Clustered broom — Cytisus aggregatus
· Beanii's broom — Cytisus x beanii Dallim.
· Dallimore's broom — Cytisus x dallimorei Rolfe.
· Decumbent broom — Cytisus decumbens (Dur.) Spach.
· Hairy, spreading broom — Cytisus hirsutus L.
· Kew broom — Cytisus x kewensis Bean.
· Blackening broom, blackening sharp-keeled broom — Cytisus nigricans L.
· Early broom — Cytisus x praecox Wheeler ex Bean.
· Prostrate broom — Cytisus procumbens (Willd.) Spreng.
· Purgative broom — Cytisus purgans (L.) Spach.
· Purple broom — Cytisus purpureus Scop.
· Regensburg broom — Cytisus ratisbonensis Schaeff.
· Russian broom — Cytisus ruthenicus Fisch.et Woloszcz.
· Broom, twiggy broom — Cytisus scoparius (L.) Link.
· Supine broom — Cytisus supinus (L.) Link.
· Variegated broom — Cytisus x versicolor (Kirchn.) Dipp.
· Erect broom — Cytisus emeriflorus Rchb
· Elongated broom — Cytisus elongatus
· Sessile-leaved broom — Cytisus ssessilifolius L.

Cultivars: ’Boskoop Ruby’, ’Burkwoodii’, ’Hollandia’, ’Lena’ , ’Zeelandia’.

Hybrids:

· +Laburnocytisus ’Adamii’ (Laburnum anagyroides + Chamaecytisus purpureus)
· Cytisus ×beanii G.Nicholson (Cytisus ardoini × Cytisus purgans)
· Cytisus ×czerniaevii Krecz.
· Cytisus ×dallimorei Rolfe (Cytisus multiflorus × Cytisus scoparius)
· Cytisus ×praecox Beauverd (Cytisus multiflorus × Cytisus purgans)
· Cytisus ×syreiszczikowi V.I. Krecz.
· Cytisus ×vadasii J.Wagner
· Cytisus ×versicolor Dippel (Cytisus hirsutus × Cytisus purpureus)
· Cytisus ×virescens Beck
· Cytisus ×watereri Wettst.

Hardiness zone: zone 5-8 (-25°C). Most species overwinter without shelter. Some require winter protection with conifer boughs. If one-year shoots are frozen in severe winters, shrubs recover quite easily. Hybrid cultivars are recommended to be sheltered with conifer boughs.

Site: very light-loving. The best planting location is an open area with a southern exposure, preferably protected from cold winds. It is not recommended to plant near ponds with fish.

Pruning: after flowering it is recommended to cut back spent shoots by half, without cutting into old wood.

Propagation: by seeds sown in spring after a 2-month stratification, and by softwood cuttings in summer. Cultivars can be propagated by grafting onto Laburnum rootstocks.

Soil: drought-tolerant, does not tolerate prolonged waterlogging or overwatering. Does not like clay soil. Not demanding to soil fertility, can grow on any garden soil, including very poor soils. Prefers slightly acidic soil. Optimal soil pH 6.5 — 7.5.

Planting: soil mix — one part sand and the other part of turf soil, peat-compost or humus; a complete mineral fertilizer or Kemira-Universal can be added (120 g per 1 m2). Does not like transplantation. Recommended spacing between plants — 30-50 cm. The root collar at ground level. Drainage is mandatory (on heavy soils — layer 15-20 cm, on light soils — 10 cm). After planting, mulch the root area with soil or peat to a depth of 3-5 cm.

Care: does not require watering. For better flowering it is recommended to fertilize the plant twice a year — first in spring, second — before flowering. In spring apply urea (20 — 30 g per 10 l water), in summer — 60 g granular superphosphate and 30 g potassium sulfate. To stimulate growth, wood ash can be applied — 200 g per bush. Cultivate no deeper than 8-12 cm.

Diseases: Powdery mildew (treat dormant buds with copper sulfate (5%), in summer regular treatments with fungazole, copper-soap solution, colloidal sulfur (0.8%) alternately), Black spot (treat dormant buds with iron or copper sulfate; in summer spray with fungazole, polycarbacin (0.2 — 0.4%), copper oxychloride (1%), captafol (0.5%), Bordeaux mixture (1%)).

Pests: broom moth (spray with chlorophos (0.2%)), broom inchworm (treat with organophosphorus or bacterial insecticides).

Companion plants: junipers, heather, groundcover perennials, ornamental grasses.

Uses: a good honey plant. Looks attractive as a solitary specimen or in group plantings, in rock gardens, in front of dark conifers, in containers, on slopes.