A strikingly beautiful group of deciduous trees and shrubs, grown for their richly coloured foliage and fragrant pea like flowers.
Family: Papilionaceae or Leguminosae
(Fabaceae in the USA)
Botanical Name: Robinia
Common Names: false acacia, rose acacia, black locust.
Foliage: Yellow or green pinnate leaves. Deciduous.
Flowers: White or pink (depending on variety), fragrant, often followed by seed pods. Not all varieties are free flowering.
Flowering Period: Spring, early summer.
Soil: Moist but well-drained, moderately fertile. Chalk, clay, sand or loam. Any pH. Will tolerate poor dry soils.
Conditions: Full sun, any aspect, sheltered from strong winds.
Habit: Bushy, fast growing, suckering.
Type: Medium-sized deciduous tree.
Hardiness: Hardy in UK.
Ideal as a specimen tree. Provides good contrast against other darkly coloured shrubs. All varieties grow well in poor soil and can tolerate dry conditions. Large types should be given adequate space in which to grow.
Plant pot grown plants during autumn and winter. Water the pot well and allow it to drain before planting. Dig a hole that is at least twice the size of the pot. Drive in a support stake to one side of the hole. Remove the plant from the pot and tease out some of the roots. Position the plant in the hole against the stake, so that the top of the root ball is level with the surrounding soil. Replace the soil, to which should be incorporate a good bucketful of planting compost and a handful of general fertiliser. Firm in well and secure the trunk of the tree to the stake with a buckle type tree tie. Water well until established.
Drought tolerant once established and generally low maintenance. A handful of general fertiliser can be sprinkled around the tree roots in the spring.
Branches are brittle and can be damaged by strong winds. Cut out any damaged wood in late summer or early autumn. Remove suckers where necessary in the autumn.
Generally disease and pest free. May be susceptible to frisia dieback.
Increase by removing rooted suckers in the autumn. Seeds of R. pseudoacacia can be sown in the autumn.
There are a number of attractive varieties available in UK garden centres. Robinia pseudoacacia 'Frisia' is one of the main varieties sold. Robinia hispida (shown below) provides an attractive medium sized shrub for smaller gardens.
Robinia pseudoacacia (see main image above). Maximum Height 80ft (25m), spread up to 50ft (15m). Green oval pinnate leaves, through which clusters of fragrant creamy white flowers hang in spring.
Robinia pseudoacacia 'Frisia' (golden false acacia) has rich yellow leaves in early spring that mellow to a greenish yellow in summer, and turn a lovely golden colour in autumn.
Robinia kelseyi is a more compact growing variety (height: 8ft/2.5m) with deep pink flowers in early summer. Makes a good standard tree if pruned correctly.
Robinia hispida (rose acacia), also grows to around 8ft/2.5m, with dark green leaves and rose pink flowers. Can be trained against a wall.