Well done if you got yesterday’s mystery plant: it was Hibiscus syriacus ‘Oiseau Bleu’, more commonly known as ‘Blue Bird’. It is my favourite of the established cultivars and I would rank it among my top 20 shrubs. But there is, as always, a catch and a caveat!
While this hardy shrub does not have quite the flamboyance of the tender Hibiscus rosa-sinensis with its often huge flowers, myriad colours and combinations and evergren leaves, it still has pretty large and showy flowers and for a couple of months in late summer, making a pleasant relief to endless buddleias!
Sometimes called rose of Sharon (but not by me) it is thought to come from China or India and was cultivated in Britain since the 16th century, which makes it one of the longest established introduced shrubs. Despite the species name it is not native of Syria but has long been grown there and Linnaeus knew it as Syrian ketmie.
It does thrive in hot climates, and on one of my infrequent visits to France, I saw marvellous examples growing the Loire valley where it obviously loved the heat. Winter cold will not harm it but it does need sun and warmth in summer to ripen the wood and to help the development of buds. In cool, wet summers and in northern gardens it sometimes fails to make buds or the buds will not open. In these cases you should either give it the sunniest spot you can find or grow it against a sunny wall. It does not need to be trained as such but will benefit from the reflected and stored heat from the wall.
‘Oiseau Bleu’ was bred in France by Croux Fils and was introduced in 1958 and soon after got its Award of Merit and later a full Award of Garden Merit.
One problem with Hibiscus syriacus is that it comes into leaf very late in spring. Even if you do know it is slow out of the chocks it still sometimes causes a few fretful weeks in May when you think it has given up the ghost. Buds form on the new growth in July and, with luck, the flowers open in August and September. Unfortunately the substantial flowers drop off and make a bit of a mess. As flowering ends the leaves turn yellow before they drop. Because the flowers are formed on new growth you can give the plant a prune in spring and you can keep it as neat as you want. Although it is potentially a large shrub 3m high you can easily keep it half that height with pruning. When it comes to soil, it really is not fussy and it is good for poor and dry soils and thrives on chalk too but it will not thrive in moist or wet soils. Clay is not an issue as long as it is not soggy.
I have never been a fan of double hibiscus because the mass of petals corrupts the intricacies of the stamens and stigmas and covers the glorious veins in the centre of the flowers. They sometimes have trouble opening too and the widely available ‘Purpureus Variegatu’ is a useless thing. Although the leaves are attractively variegated the densely double buds never open (in my experience). It must cause endless disappointment. Some of the more recent cultivars are more successful and the British-bred ‘Chiffon’ range are not too dense and seem to do well. They are not for me and I will stick with the two ‘Oiseau Bleu’ in the front garden. ‘China Chiffon’ (‘Bricutts’) is below.
8/10 – not pretty in winter – needs warmth