Move over Hawaii, we have our own beautiful hibiscus to light up our summer gardens. Perhaps one of the most under-used summer flowering shrub is the hardy Hibiscus syriacus althaea or Rose of Sharon. It has been cultivated in England since the 16th century, but it is only over the past few years that, because of today’s many new varieties, it has become a more mainstream plant.
Hardy to zone six, and possibly some high zone fives, it is one of the few flowering shrubs that opens in succession from July through to October. Once the mophead hydrangeas finish, there is a distinct lack of garden colour from flowering shrubs, and that’s why these plants are so important. Hibiscus are generally the last flowering shrub to show leaves in spring but they more than make up for it by being the last hurrah in the fall garden.
Hibiscus can be somewhat difficult to get established. They need full sun or just a touch of shade and a little tender loving care to get going and to perform their best. Hibiscus grow just fine in a wide variety of well drained soils, but they need plenty of organic matter to hold moisture. They wilt easily in hot weather and need a deep watering during periods of long drought. Don’t move them around the garden as they are not happy being transplanted. It’s also a good idea to mulch their roots over the first couple of winters to protect them from deep frost.
Hibiscus are usually sold as small to medium sized plants in bush form, but they can also be purchased or trained into a handsome tree form. Growing to about 3.5 meters (12 feet), they can easily be pruned in late winter to conform their size to your garden needs. There are three flower forms: large singles, semi-double and smaller doubles. My favourite is ‘Red Heart’, a large white single with a red eye that really shows up in the garden. ‘Diana’ is a huge pure white triploid that remains open at night. ‘Woodbridge’ is a single magenta rose with a red eye. ‘Bluebird’ and ‘Marina’ are improved forms of a single blue with a red eye. In the double forms, ‘Ardens’ is a purple and ‘Collie Mullens’ is a magenta rose with a crimson eye.
The newest series from Proven Winners is the ‘Chiffon Series’ featuring beautiful large, full semi-doubles. The blue, lavender, white and pink ‘Chiffons’ are quite spectacular. Some very innovative growers are planting two colours together in one container, providing a beautiful two tone effect for a novel addition to any garden.