There are two main species that share the common name Broom: Genista and Cytisus. Both are very similar in appearance but the main differences are only truly distinguishable by botanists. Both forms can be grown under similar conditions but Genistas are more tolerant of lime.
Family: Fabaceae (legume) or Leguminosae
Botanical Names: Genista and Cytisus
Common Names: Broom
Foliage: Evergreen or deciduous, small, usually lanceolate, green leaves.
Flowers: All bear pea like flowers, mainly in shades of yellow. A good range of cultivars are available in various hues of white, yellow, orange, pink and red.
Soil: Well-drained poor soil (clay, sand or loam), preferably acid.
Conditions: Best in full sun but will tolerate some light shade. Planting aspect and location depend on variety.
Habit: Lax, bushy, fast growing.
Type: Small to medium sized shrub.
Origin: Mediterranean, western Europe and North Africa.
Hardiness: Brooms are reasonable hardy in the UK but need protection in very harsh winters.
Best grown in an open, sunny position, in a well-drained, poor soil. Cytisus dislikes thin alkaline/chalky soils but Genista is more lime tolerant.
Brooms look there best when in full bloom at the front of other green shrubs or when planted en-masse down a bank. Dwarf forms are ideal for the rock garden.
Plants grown in too much shade will become leggy and don't flower well.
Water thoroughly during dry weather until well established. Mulch with ericaceous compost in spring if the soil is alkaline.
Many brooms are short-lived but they can be extended and improved using the correct pruning methods.
Cytisus are generally pruned annually once flowering has finished. Varieties that flower on last year's growth should ideally be cut back by two-thirds. Varieties that flower on this year's growth should be pruned in early spring.
Cytisus battandieri should be pruned more like a woody shrub by removing any dead, damaged or disruptive shoots after flowering. Wall trained forms should have shoots removed that are growing at right angles to the wall and by cutting back any branches that have grown too long.
Pruning of Genistas depends on the variety, for example:
Genista aetnensis can be cut back several times each season to make it bushy.
Genista hispanica can be lightly sheared after flowering.
Genista lydia does not need to be pruned.
Susceptible to attack by gall-mite.
Can be affected by fungus dieback, which causes black spots on leaves and stems.
Sow seed under cover in March or outdoors in April. Presoak seeds before sowing and germinate at 18°C/65°F. Protect early sowings under a cloche or cold frame.
Alternatively, take 3in (7.5cm) long heel
cuttings of ripe growth in
summer. Root slowly in a cold frame.
Brooms are generally a robust group of hardy shrubs, from miniature forms suitable for the rock garden to large shrubs for the border.
Cytisus ardoinii is a prostrate alpine shrub covered with yellow flowers in spring. Height to 5in (12cm).
Cytisus battandieri (pineapple broom or Moroccan broom) is not typically broom-like in form but more of a medium woody shrub. It has large trifoliate silvery leaves and bright yellow cylindrical flower clusters from May to June. The flowers are strongly pineapple-scented, hence its common name. Not fully hardy in the UK. Protect in severe winters or grow against a south-east or west-facing wall. Height to 15ft (4.5m). Give it plenty of sunshine or the flower display will be disappointing. Can be also trained as a standard or small tree.
Cytisus 'Burkwoodii' is a good hybrid form with cerise and crimson flowers in late spring. Height to 5ft (1.5m).
Cytisus x kewensis is a wide, low growing, deciduous shrub, with pale yellow to creamy white flowers in spring. Excellent for rock gardens. Height to 2ft (60cm).
Cytisus x praecox (Warminster broom) has pale yellow flowers in early May. Good varieties include 'Allgold' with deep-yellow flowers covering its arching branches. Height to 5ft (1.5m).
Cytisus scoparius (common broom or Scotch broom) provides a good show of yellow flowers in May-June. Height to 5ft (1.5m). Modern hybrids provide a wider range of flower colours, such as 'Andreanus' with deep brown red and yellow flowers; 'Cornish Cream' with ivory cream and yellows flowers; 'Goldfinch' with crimson and yellow flowers, with pink and yellow wings and 'Killiney Red' with a smaller, compact habit, and red blooms.
Genista aetnensis (Mount Etna broom) is a tree-like shrub with linear leaves and yellow flowers in July. Height to 10ft (3m), spread to 8ft (2.4m) and more. Not completely hardy in the UK.
Genista hispanica (Spanish gorse) is a dense, spiny, gorse like shrub. Its brilliant golden flowers cover the plant in June-July. Height to 3ft (90cm), spread to 7ft (2.1m) and more.
Genista lydia has green arching stems, dripping with golden yellow flowers in May-June. Height 2ft (60cm), spread 3ft (90cm).
Spartium is yet another of the garden brooms, it is a monotypic genus (single species) of the family Fabaceae.
Spartium junceum a vigorous
open shrub with tall green arching stems bearing bright
yellow flowers, often fragrant. Not fully hardy in
the UK. No
pruning is required. Tolerant of chalky soils. Height
to 7ft (2.5m).