Amorpha fruticosa

RHS Plant Profile
bastard indigo

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bastard indigo RHS 2002
bastard indigo RHS
bastard indigo RHS
bastard indigo RHS
bastard indigo RHS
bastard indigo RHS

Other common names

river forest, river locust, shrubby false indigo, false indigo

Synonyms

Amorpha croceolanata
Amorpha occidentalis
Amorpha tenessensis
Amorpha angustifolia
Amorpha virgata
Amorpha fragrans

Shrubs
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A vigorous deciduous shrub of spreading habit, with leaves composed of up to 30 oval leaflets, and slender racemes to 15cm in length, of deep purple flowers with orange anthers

Position

Full sun, Partial shade

Soil Types

Loam, Sand

Max Height

2.5-4 metres

Max Spread

2.5-4 metres

Size

Time to Maturity
10–20 years
Max Spread
2.5-4 metres
Max Height
2.5-4 metres

Growing Conditions

Loam Sand
Moisture
Well–drained
pH
Acid or Alkaline or Neutral

Position

Full sun Partial shade
Aspect
West–facing or East–facing or South–facing or North–facing
Exposure
Exposed or Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

  • H1A: under glass all year (>15C)
  • H1B: can be grown outside in the summer (10 - 15)
  • H1C: can be grown outside in the summer (5 - 10)
  • H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
  • H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
  • H4: hardy through most of the UK (-10 to -5)
  • H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
  • H6: hardy in all of UK and northern Europe (-20 to -15)
  • H7: hardy in the severest European continental climates (< -20)
H6
Drought Resistance
Yes

Colour & Scent

Season Stem Flower Foliage Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family
Fabaceae
Native to GB/Ireland
No
Foliage
Deciduous
Habit
Bushy
Genus
Amorpha are deciduous shrubs with pinnate leaves and racemes of tiny, single-petalled, deep purple or blue flowers in summer
Name Status
Correct
Plant Range
S USA

How to Grow

Cultivation

Grows well in light sandy soil and can survive in very poor soils. Tolerant of extreme cold

Propagation

Propagate by seed in autumn. Seed must be scarified as they have hard seed coats. Use sandpaper or a file to scarify (abrade) the seed coat. Chit the seed either by using a knife to nick the seed coat or by soaking the seed in warm water for 24 hours. Care should be taken when soaking seed, as too much can cause rotting. Sow at any time of year 2mm deep in moist, free-draining, quality seed compost. Propagate at 10-15C in a greenhouse, on a windowsill or in a coldframe outdoors in spring. Germination should take place in 30-120 days

Suggested planting locations and garden types

  • Low Maintenance
  • Flower borders and beds

Pruning

Pruning group 6

Pests

Generally pest-free

Diseases

A rust may occur (N. America only)