Amorpha are a genus of north American deciduous shrubs and two species, A. canescens – lead plant, and A. fruticosa – bastard indigo, appear from time to time on the Burncoose website. In the wild they grow in dry scrubby areas on prairies and hills. They thrive in poor soils and will tolerate extreme cold. In the UK they are therefore sturdy border shrubs although A. canescens will grow only up to 3ft tall (with a 5ft spread) while A. fruticosa can grow up to three times this size overall in maturity. Both species have aromatic leaves with alternate pinnate leaves and small, terminal, upright racemes of pea-like flowers with only a single petal.
A. canescens produces hairy grey-white shoots in spring and summer with violet-purple or purplish-blue flowers that have orange anthers. The flowers appear in 6in racemes in late summer or on into early autumn.
A. fruticosa also has purple-blue flowers with orange or yellow anthers but these appear earlier in the summer in profusion leaving brown upright seed heads on into the autumn.
These plants will grow well in sun or partial shade in poor soils. They are readily grown from seed (as are most plants with ‘pea’ flowers when presoaked in water) in containers in the cold frame in autumn. A. fruticosa can also be propagated readily from root suckers.
Amorpha need to be pruned back hard at the end of the growing season or in the spring to about 12-18in above ground level. This rejuvenates the plant and encourages a good display of flowers on soft young new growth. Without pruning there may well be stem dieback and a much more sparse display.
