Hibiscus syriacus and its many different coloured flowering forms are common plants in the gardens of south London and in the hotter counties of SE England but they are not so common in West Country gardens where rainfall levels are higher. There is a good reason for this in that H. syriacus needs long hot summers to flower decently. With global warming and record summer temperatures in 2019 they may well now become more widely grown.
H. syriacus are upright deciduous shrubs which can grow up to 10ft tall but are generally rather less than this in height although they can (without pruning) develop a sizeable spread too. The leaves are ovate to diamond shape with three lobes and about 4in long. Large trumpet shaped flowers, 3-4in across, appear in late July and through to September in a good hot summer. The old flower heads shrivel up on themselves while still retaining some colour and the plant often has a slightly untidy appearance although each individual flower is well worth it.
H. syriacus ‘Blue Bird’ has bright blue flowers with small red centres. ‘Woodbridge’ has rich pink flowers and ‘Diana’ has large pure white flowers with crimped or wavy margined petals.
These hibiscus can of course be grown in the greenhouse as well as in a hot dry sunny position in the shrub border in neutral or slightly acidic soil. Under glass they need humidity, good ventilation and filtered light to perform well. Feeding in the flowering months is important and be careful not to overwater them while dormant in winter.
We have very seldom seen our hibiscus set seed in the nursery but they will root from greenwood cuttings in late spring or riper new growth cuttings taken in the summer. The plants can also be layered.
