Celebrate the year of the hardy hibiscus
Hardy hibiscus adds a splash of tropical flair to your perennial garden
Hardy hibiscus adds a splash of tropical flair to your perennial garden. With notes from the National Garden Bureau (www.ngb.org), let’s take a closer look at the garden workhorse.
Fast-growing and fabulous, these plants explode with pinwheel-like flowers that can reach the size of dinner plates in late summer. Often confused with their tropical cousins, these plants are actually capable of surviving temps as low as –34 C.
North American gardeners can feel assured knowing they are planting a native perennial. Hardy hibiscus are hybrids that can be primarily traced back to the species hibiscus moscheutos. This species can be found growing naturally in wetlands and along riverbanks throughout the Midwest and East Coast, even into Ontario and extending down even into Texas and Florida.
Know your hibiscus
Hibiscus is both the common and botanical name for a few different popular classes of the plant. Most think of tropical hibiscus (hibiscus rosa-sinensis) when they hear the word, while horticulturists may note the shrub rose of Sharon (hibiscus syriacus) also falls in this category. However, neither of these plants fall into what is commonly considered “hardy hibiscus.”
Here is a quick overview of how they differ:
HARDY HIBISCUS
This set of plants primarily includes the species native to North America (such as hibiscus moscheutos and hibiscus laevis), and hybrids of those species. These plants are true perennials, tend to have the largest flowers, and die back to the ground each year.
SHRUB HIBISCUS
Also called rose of Sharon, most frequently refers to the species hibiscus syriacus which is native to southern and central Asia. Rose of Sharon has a woody habit and blooms on the same structure each year. These tend to be the largest in size with some varieties getting 4.5 metres tall.
TROPICAL HIBISCUS
Or hibiscus rosa-sinensis, are from Southeast Asia and are technically a shrub like their cousin, hibiscus syriacus, though significantly less hardy. These varieties work as patio or house plants here in Ontario since they are not frost tolerant.
Common varieties to keep your eye out for
Hardy hibiscus comes in shades of white, pink, red, and yellow, with different eye patterns and streaking through the petals. The leaves of the plants can also vary in colour from green to bronze to near-black. Some of the most popular varieties available include: Summer Spice Series, Luna Series, Head over Heels and Summerific Series.
Look for hardy hibiscus in the perennials section of your local nursery. They should not be planted out in the garden until all danger of frost has passed (about the same time you would plant tomatoes and peppers.) Our local Stokes Seed (www.stokeseeds.com) offers hardy hibiscus seeds (Luna White and Luna Red are both available on their website, a packet of 10 seeds $8.90). Sow outdoors in spring for bloom the following year.
Water, wait and give them space: How to’s for happy hibiscus plants
Hardy hibiscus have a history of growing in wet areas such as along riverbanks and around inland lakes. They perform best with consistent watering, particularly if they have been recently transplanted.
If your hibiscus is losing its lowest leaves or aborting buds, you may need to up the water. This watertolerant characteristic makes them perfect for areas of the garden that periodically flood, or as a thriller in rain gardens.
Another characteristic of the genus is they are late to break dormancy in spring. They’re not dead! When they do wake up they’re off to the races growing more than an inch a day. Depending on the year, hibiscus may stay dormant through the end of May or even into early June.
It’s a good idea to leave about 15centimetres of the previous year’s growth standing when you do the spring garden cleanup. The stems will remind you to keep an eye out for the late-emerging hibiscus. My hibiscus share a bed with tulips, daffodils and forget-me-nots that will be out of bloom when the hibiscus makes an appearance. As an added bonus, the tired foliage of these spring-blooming bulbs will quickly be covered by the wide spread of the hibiscus.
Hibiscus habits
Give hardy hibiscus plenty of space to grow. Depending on the variety, mature hibiscus can get 1.5 m wide and grow quickly during the year. If you take a week’s vacation in June, you’re likely to come back to a plant twice the size you left it.
Full sun is a must. In too much shade the otherwise sturdy habits stretch and get floppy. Over shading will also lead to a decrease in bud count and diminished flowering performance. UV light (full sun) will also bring out the dark foliage colours.
In my Niagara garden, I planted three seed-grown hardy hibiscus more than 25 years ago. One of the seedlings did not make it, a second seedling succumbed when it was transplanted some 10 years after planting (they resent being transplanted or divided), and the third plant still blooms on cue, usually in late July and into the autumn. At first, I disliked the luncheon-plate sized, red flowers — they looked gaudy. But it’s hard to dislike a plant that comes back year after year and puts on a good show with very little prompting.
For the past couple of years, my hardy hibiscus did not appear until mid-june, growth and flowering were noticeably diminished. I now realize the shade and the thirsty roots of a nearby sweet gum tree are probably at fault — the hibiscus is starved for light and water. The tree isn’t going anywhere soon, so it’s time to plant another hardy hibiscus in a more forgiving spot in the garden — with so many new varieties on the market, I may have to try more than one hardy hibiscus this year.