It’s much easier to have a colourful and visually interesting garden in say, June, than right now in the heat of August. We’re in a transition phase; the late spring and early summer colour explosion has passed and given the hot temperatures we’ve received for the past month it’s amazing that anything looks good out there. Some plants are all the more valuable because they do provide us with blooms during these times and perhaps the showiest of these is the Hardy Hibiscus, aka the Rose of Sharon.
This large flowering shrub is not a rose at all, but a species of the Hibiscus, the popular tropical flower that lasts only one day. Hibiscus syriacus is native to eastern Asia and as a woody deciduous shrub it’s hardy to Zone 5, surviving temperatures as low as -25 deg. C. Because it’s so late to leaf out in the spring we often have calls from customers in April who are concerned that their Hibiscus hasn’t survived the winter. Often they won’t leaf out right to the end of the stems after an especially cold winter, but that’s not an issue as they bloom on current season’s growth anyway. They’re a lot tougher than they look!
Fortunately for us Hibiscus syriacus loves hot climates. Once the temperatures begin to warm in spring they grow rapidly, and if they’re located in moist, but well-drained soil in a sunny location they’ll develop a heavy set of flower buds which burst open beginning in late July. Although the flowers only last a day they continue to bud and bloom well into autumn, lifting the garden at a time when it can really use a lift.
The popularity of the shrub hibiscus is a relatively recent phenomenon, stretching back to the 1970’s. When the so-called “Greek Goddess” series was introduced they featured more vigorous growth, larger flowers and fewer seedlings and now varieties such as Minerva, Aphrodite, Helene have been joined by several other cultivars that have single or double blooms, darker centres and colours ranging from pure white to red, lavender and blue-lilac.
Hibiscus syriacus definitely falls into the large shrub category, as they will grow 2.5 metres tall with erect, upright branches. The tree form, trained as a standard, is a great choice for small gardens and I’ve seen them used as street trees in Italian towns.
The next frontier in shrub hibiscus is developing more compact plants that will fit into mixed shrub or perennial borders. In the meantime, the large specimens we see in the garden centres and landscapes in full bloom right now are wonderful privacy screens or feature shrubs that dominate a late-summer garden like no other flowering shrub.