Tag: Guinea Impatiens

  • Problem-solving SunPatiens catch the eye

    Problem-solving SunPatiens catch the eye

    SunPatiens come in range of vivid colours, too. (Photo from Sakata Ornamentals)
    SunPatiens come in range of vivid colours, too. (Photo from Sakata Ornamentals)

    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.

  • Monitoring downy mildew on impatiens

    Monitoring downy mildew on impatiens

    Fortunately, New Guinea impatiens is resistant to downy mildew.  (Photo from Veseys.com)
    Fortunately, New Guinea impatiens is resistant to downy mildew.  (Photo from Veseys.com)

    For years  every garden centre and corner grocery store has been flaunting flats of bright impatiens seedlings. It would be fair to say impatiens is overplanted, but their vivid colours and generous floral displays are hard to resist. Unfortunately, impatiens is being threatened by a devastating mildew disease that destroys every leaf, flower and bud, regardless of whether it’s grown in a container or in the ground.

    I’ve seen impatiens afflicted with downy mildew over the years, but never the full destruction of plants as recently reported. Infections in the United States are widespread, and the disease pathogen (Plasmopara obducens) has also been positively identified in Ontario, Quebec and British Columbia. (An Internet search for “impatiens and downy mildew” will turn up lots of information.) This strain of downy mildew is specific to both single and double garden impatiens (Impatiens walleriana), or busy lizzies as you might call them, but doesn’t infect other kinds of impatiens. New Guinea or sun impatiens (I. hawkeri) is resistant to it.

    Downy mildew is encouraged by excessive watering, high air humidity and relatively low temperatures, between 15 and 23°C. Midsummer drought conditions with low humidity and high temperatures may help to stave off mildew infections, while moist spring and late summer weather will encourage the disease. Once disease spores are present, it’s almost impossible to prevent infection from spreading. Downy mildew on impatiens is spread two ways: short-lived dispersal spores produced in the white powdery coating on the undersides of leaves are dispersed by wind and water splashes; and survival spores (called oospores) that are produced inside stems and petioles, and deposited in the soil. Spores in the soil can overwinter, and will infect new plants the following season.

    Initial symptoms of downy mildew on impatiens usually occur in moist conditions with cool nights, beginning with the youngest foliage, causing leaves to appear yellowed, slightly chlorotic or stippled, and often with a thin, white downy coating on the leaf undersides. The white powder can also be found on the undersides of leaves still green. Affected leaves fall off, leaving bare stems.

    Fungus infections are difficult to control, and the only effective treatment is preventative. A preventative spray program every two weeks from the day of planting until the end of the growing season is required to provide protection before fungus spores become established on foliar tissue. A mixture of one tablespoon (15 mL) light horticultural oil (available at garden centres) combined with one tablespoon of baking soda per gallon (4L) of water, sprayed on all sides of the leaves and stems every two weeks, is effective in preventing infection.

    Impatiens plants that are produced in greenhouses are likely disease free when they arrive at the market. However, once planted in the open garden, weather conditions may trigger the deadly downy mildew spores. What should we do about this? Will it be necessary to ban impatiens from the garden? Well, I’m still going to plant them, and certainly hope for the best. But unlike other years when I’ve given little regard to planting conditions and still had gorgeous flower displays, I’ll now give more consideration to how I plant my impatiens.

    I can’t control air temperature, but perhaps I can do something about water and humidity. This year I won’t set impatiens plants so close together as I have in the past. Leaving more space between individual plants will help to lower humidity and increase air circulation. I won’t water impatiens from overhead, but instead will flood the ground and avoid wetting the foliage. Any sick plants will be immediately removed and disposed of in garbage; and during fall cleanup, all impatiens plant parts – stems, flowers, and root balls – will be lifted, but not composted (mildew spores can live in compost).

    This is something like treating impatiens with all the fuss of hybrid tea roses. But I’m willing to keep growing impatiens, just so long as they’re healthy and happy in my garden.

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