I was recently surprised to see a display of large and vigorous impatiens plants, looking so robust that I had to check their tags to be sure I wasn’t mistaken. They were SunPatiens, a new strain of New Guinea impatiens (Impatiens hawkeri) that has been bred with wild impatiens species to produce hybrid plants with an impressive list of assets. SunPatiens thrive in full sun to part shade, bloom from spring to frost, have three-inch (8-cm) wide flowers, and come in a broad range of pastel and vivid colours and foliage designs. They’re also highly resistant to downy mildew and will tolerate heat. SunPatiens could be the answer to all our impatiens woes, since traditional impatiens (I. walleriana) was massively struck with a debilitating water mould infection.
The downy mildew disease (Plasmopara obducens) decimating I. walleriana has reduced their availability in nurseries, leaving gardeners with limited choices and in the lurch. The infection is brought into gardens on infected nursery plants, and is untreatable once it appears on foliage. The disease spores can overwinter in garden soil, and will infect the next season’s plants.
If you’ve grown traditional impatiens in the past couple of years, you would probably recognize the midsummer symptoms: wilting or drooping light yellow or stippled foliage; a fluffy white coating on leaf undersides; and blossoms and leaves dropping off, leaving bare stems that eventually collapse. [How to monitor for downy mildew disease.]
Impatiens have long been shade garden workhorses, bringing brilliant colour and generous flowers to areas where little else blooms. Frequently, impatiens were used as carpet-bedding plants, with dozens of flats purchased to cover expansive ground areas. That over-use may have been the tipping point on the virulent disease that’s now mowing down standard garden impatiens. The monoculture created by hundreds of plants growing shoulder-to-shoulder in many parks and gardens set the stage for swift replication of disease spores that have continued to live in infected soils.
The progression of improved impatiens plant breeding has been accomplished quite quickly over the past two decades. First, we had the standard impatiens (I. walleriana) that excels mostly in shade to part shade and cooler temperatures. New Guinea impatiens (I. hawkeri) arrived, with larger flowers, brightly variegated foliage and ability to accept more sun, though not a hot, full-sun location. Now we have SunPatiens, which will accept both part shade to full sun, tolerates heat and humidity, has strong disease resistance, and carries the largest flowers of all. It seems SunPatiens is the right plant, at the right time. They won’t be the solution for full shade, but are certainly the best impatiens for part shade to full sun. [Editor's note: In Garden Making's 15 new plants for 2012 we included SunPatiens Carmine Red.]
I selected white SunPatiens with green foliage, because I’ve been looking for a plant with consistent white presence for the growing season. I’ve put them into a full sun bed with mostly purple and red salvia, penstemon and butterfly bushes. The blazing white flowers are the largest I’ve ever seen on impatiens, and it looks like the plants will be consistently loaded with buds and blooms. They were also available with fancy yellow-and-green variegated foliage, but that was a bit more colour excitement than I need. A look at the breeder’s web site (sunpatiens.com) shows a full palette of flower colours, and I particularly covet the coral and electric orange selections.
Breeders of SunPatiens have one more trick up their sleeves: the plants come in three sizes. My variety is in the compact category (24 x 24 inches / 60 x 60 cm), which is upright and fits well into a bed with perennials. There are also varieties with a spreading, mounding habit (30 x 36 inches / 75 x 90 cm) to fill hanging baskets or bed areas, and a vigorous form (40 x 40 inches / 100 x 100 cm) that grows into an upright vase-shape. The plants are self-cleaning, and like all impatiens, require consistently moist soil.
Here is one small secret to seal the deal on SunPatiens impatiens: they root rapidly from cuttings. Cuttings set thick root clusters, and give you a few new plants to take inside to a sunny window and enjoy over winter.
Enough said. Get some.