New Perennial Rose Mallows

Spectacular new hybrids of an old garden favourite will soon become available to gardeners. Better still, they arise from increasing interest in native North American plants. Now its time for hardy herbaceous hibiscus to shine even brighter in the perennial border.

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Swamp Rose-Mallow, Hibiscus moscheutos, is found sparsely today from southern Ontario south down through the central U.S. and Atlantic states into Texas, preferring rapidly-dwindling wetlands. The spectacular blooms, 15cm (6-inches) across, vary from white through pink to a deep rose, usually with an eye of deep purple or red, depending on the various forms. The plants themselves may reach 2m (6?-feet) if they are lucky forming large colonies. Although the Rose Mallow attracts attention in public gardens and garden centres wherever it occurs – modern blooms may be 30cm (one foot) in diameter – it rarely emerges before late May or early June. Flowering time is from July until cut back by frost. In northern gardens it is advisable to mulch overwinter but this must be removed in spring before slugs seek to feast on the tender young shoots. Rose Mallow makes up for all this by tolerating a wide range of soils in sun or light shade. It does best, however, in compost-rich light loams sheltered from strong winds. In acknowledgement of its marshy origins though it must by kept constantly moist. Amateur and professional hybridizers have been interested in H. moscheutos and several of its North American relatives. The Halberd-Leaved Rose-Mallow, H. militaris, for example, has pink flower with a purple eye, found on river banks and marshy areas from Minnesota south. Similarly the Crimson-eyed Rose-Mallow, H. palustris, from brackish or Atlantic coastal marshes, H. coccineus and H. dasyacalyx – amongst others. The late Georgia Bost developed several new cultivars on her Hibiscus Hill Plantation in Waller, Texas, showed that such species could naturally hybridize. “The introduction of a purple colour in ‘Plum Crazy’ by Flemings Brothers in 1999 was an important progress in winter-hardy hibiscus breeding,” explained Dr. Dariusz Malinowski of Texas A&M AgriLife, Vernon in a press release last November.

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With his two colleagues, Dr. William Poinchak, AgriLife Research animal nutritionist, and Steve Brown, Texas Foundation Seed Service program director, both based in Vernon, Malinowski continuously works on creating new colours in winter-hardy hibiscus. The last few years have proven prolific ones. “In the past six years we have disclosed to the Texas A&M University System Office of Technology and Commercialization more than 180 unique lines of winter-hardy hibiscus with very unusual flower and leaf colour and shape,” he said. ‘Blue Angel,’ the first blue-flowering hibiscus cultivar, was one such. ‘Robert Brown,’ a chimera, with an unpredictable dual-coloured pattern of the flower. The salmon colour is the third breakthrough, Malinowski said. However A. R. Buckley in 1977 recorded a salmon-pink cultivar, ‘The Clown’ as being available. Having created shades of pink, magenta, red, crimson, purple, blue, lavender and maroon, next up for the AgriLife Research breeding team is are true yellow and orange hues. There are cultivars with ‘yellow’ in their name, but these are cream at the best, Malinowski says. Don’t expect to see these for at least a couple of years. Steve Brown explains several companies are considering these for commercialization. All these are vegetatively propagated rather than from seed so it takes time to build up sufficient numbers to provide wholesale nurseries with stock to grow on in pots. Eventually, after a few years, these will arrive at local garden centres and big box stores – and into the gardens of eager homeowners. Unfortunately, back in the wild Hibiscus moscheutos is threatened with all the usual plagues of encroaching civilization. In Canada listed as a species of special concern under the Species at Risk Act.

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