Perhaps most identified with the welcoming floral wreaths of the Pacific islands, Hibiscus are in fact a huge and varied family containing 300 species of hardy and tender annuals, evergreens and deciduous shrubs. Of these, three tender evergreen are in general cultivation, but in Great Britain they will require protection so should be treated as houseplants.
Native to much of Asia, hardy hibiscus has been been grown as a garden shrub in Korea since time immemorial. In fact, it has become the national flower of South Korea where its flowers are eaten and the leaves are brewed for a tisane - whatever that is (fancy herbal tea apparently)!
For general hardiness, the strongest species is Hisbiscus syriacus and luckily for gardeners, this species comes in at least a couple of dozen colour forms. These include double flowered forms as well as some varieties which display variegated leaves!
How to grow tender Hibiscus
The most popular species is the gorgeous, evergreen Hibiscus rosa-sinensis, but unfortunately is not hardy. If you can expect winter temperatures of no less that 7-10 degrees Celsius then it can be planted outside in any ordinary well-drained garden.
Give them a sheltered position, with as much sun as possible. You can of course choose to grow it as a container specimen, in which case plant into a good quality compost such as John Innes 'No 2' or 'No 3'.
When over-wintering, try to maintain a minimum temperature of 7-10 degrees Celsius, and the soil moist, but don't be surprised if you begin to experience leaf-drop.
However the foliage will remain when temperatures can be kept above 16 degrees Celsius. Just keep the compost on the moist side in these warmer temperature and you can expect your plant to continue to flower. If temperatures exceed 21 degrees Celsius then provide plenty of ventilation.
How to grow the hardy Hibisucus
Hibiscus syriacus and its numerous varieties will thrive in any well drained, fertile soil. Fertile is the key here as this species is incredibly hungry. Even the spring new growth will emerge looking nitrogen deficient so regularly top dress with a rich compost. Failing that, give them a regular liquid feed.
If your hibiscus plant is container grow then it can be planted at ant time, just be aware that you will need to keep an eye on the watering if you decide to plant during the height of summer.
Plant in a sheltered border, but make sure that it is in a position that takes full advantage of the sun. As hardy hibiscus are late flowering, it is advisable to protect them further by growing them against a wall or the side of a house in northern gardens.
Once established, there is no need to prune your hardy hibiscus, but long shoots can be trimmed back after flowering.
Be aware that drought conditions and low night temperatures can cause bud drop