Hardy Hibiscus

Hibiscus moscheutos takes its own sweet time emerging from the ground in the spring, but when its enormous, satiny blooms finally open in late summer, it puts on quite the show. In the production of these impressive blooms, I have no doubt that summer is complicit. There is no way summer is going to fade demurely into fall. She is determined to go out with a flourish.

Hibiscus moscheutos has a bevvy common names; Rose Mallows, Swamp Mallow, Dinner-plate Hibiscus and Hardy Hibiscus. Though they look quite tropical, the species forms of Hibiscus moscheutos are a cold-hardy woodland plant native to U.S. and Canada. Here in Ontario, Hibiscus moscheutos are considered to be a native plant at risk, but a few colonies with pale pink flowers can still be found growing in the shoreline marshes of the Carolinian and Great Lakes/St. Lawrence River forest regions.

Like other herbaceous perennials, Hibiscus moscheutos has foliage and woody stems that die back to the ground in winter. They are tall, vase-shaped plants that reach an average of two to six feet in height and approximately three feet in width. Though these plants will perform best in areas with long, hot summers, they are hardy to zones 4 or 5.

The blooms of Hibiscus moscheutos consist of five flat overlapping petals and can reach up to 10-12 inches across. As well as bi-colored flowers, they come in solid shades of lavender, rose, peach, red and white.

Each individual flower opens for just one or two days and fades as soon as it is pollinated. While the flowers are short-lived, a single plant can be covered in flower buds ensuring a succession of blooms from mid-summer right up until the first frosts of fall.

A look at the foliage above and below.

Many of the cultivars have matt, medium-green foliage, but there are a few varieties have bronze or eggplant colored foliage. As Hibiscus moscheutos bloom late in the gardening season, cultivars that have this dark attractive foliage come with a definite bonus.

Hibiscus moscheutos do have one drawback– like Rose of Sharon (Hibiscus syriacus) they can self-sow and become a bit weedy. And the seedlings may not be the same color as the parent. Deadheading spent flowers is one way to limit this problem.

How to Plant

Nurseries tend to showcase hardy Hibiscus in late summer when they are in full flower, but planting them that late in the season doesn't really give Hibiscus moscheutos enough time to get properly established before winter. It is much better to take a few notes now and hold off making your purchase until next spring.

Hibiscus moscheutos do best in moist, rich organic soil. They will, however, tolerate average garden soil provided that the soil is not allowed to dry out completely. Plant them in full sun in an area that has good air circulation, but is protected from the wind.

When you do your planting, it's a good idea to add some organic material, such as compost, to your soil. A top-dressing of bark mulch will help preserve soil moisture and keep your new plant happy. Even so, deep and consistent watering is especially important during that first season.

Ongoing Care

Hibiscus moscheutos are slow to emerge in the spring, and depending on your garden's zone, may not appear until sometime in June. A layer of compost applied each spring will help encourage that fresh new growth.

Spent flowers can look a bit bedraggled, so deadhead them to keep your hibiscus looking tidy.

Every fall cut back the stems to three or four inches above the ground. In northern garden zones, it's a good idea to protect the crown of the plant with some bark or straw mulch.

Pests and Problems

• Japanese Beetles can be an annoying problem, and if left unchecked, can cause extensive damage to the foliage and flowers. The easiest solution is to knock any Japanese Beetles you find into a large jar or bucket filled with soapy water.

• Sawflies, whiteflies and aphids can also be occasional pests.

• Leaf scorch can occur if the soil is allowed to dry out completely. 

• Hibiscus moscheutos also has some susceptibility to leaf blight, rust and canker.

A few of the Cultivars Available

White Hibiscus x 'Blue River II' has large white flowers and green foliage. Full sun. Height: 120-150 cm (47-59 inches), Spread: 75-90 cm (29-35 inches). USDA zones: 4-9.

Hibiscus 'Plum Crazy' has rose-purple flowers with a dark purple eye. The foliage also has a hint of purple. Full sun. Height: 90-105 cm (35-41 inches), Spread: 75-90 cm (29-35 inches). USDA zones: 4-9.

Hibiscus 'Kopper King' has white flowers with a red eye. The foliage is a deep copper color. Mulch in late fall in zones 4 and 5 for better winter hardiness. Full sun. Height: 90-105 cm (35-41 inches), Spread: 75-90 cm (29-35 inches). USDA zones: 4-9.

Hibiscus 'Kopper King' 

Hibiscus 'Sweet Caroline' has bright pink flowers with darker pink veining and a dark red eye. Full sun. Height: 90-120 cm (36-48 inches), Spread: 75-90 cm (29-35 inches). USDA zones: 5-9.

Dwarf Hibiscus 'Luna Red' is a compact variety that has bright green foliage and large red flowers. Plant it in rich, moist garden soil. Mulch in late fall in zones 4 and 5 for better winter hardiness. Full sun.  Height: 60-90 cm (23-35 inches), Spread: 45-60 cm (18-23 inches). USDA zones: 5-9.

Dwarf Hibiscus 'Luna Rose' is similar to 'Luna Red, but has pink flowers.

Dwarf Hibiscus 'Luna White' is yet another compact variety that has white flowers with a large red eye.

Hibiscus 'Kopper King' at the Toronto Botanical Gardens.

Hibiscus 'Kopper King' at the Lucy Maud Montgomery Garden in Norval, Ontario.

There is no denying that these are magnificent flowers make a dramatic end to the summer season.

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