New Guinea impatiens resist downy mildew

June 12, 2013
New Guinea impatiens do best with afternoon shade. In hot sun the leaves can scorch and the plant will suffer.

When it comes to love the Italians have a phrase, “Chi non è impaziente non è nell’amore.” meaning “He who is not impatient is not in love.”

Impatience in the garden gives us the flower impatiens, which takes its scientific name Impatiens (Latin for “impatient”) because the seed pods explode when touched.

Besides blooming in a wide range of colors, impatiens (Impatiens walleriana) are in demand because they can grow in the shade. But love often dies, and impatiens are dying too, from an outbreak of deadly downy mildew, Plasmopara obducens.

This form of downy mildew only attacks Impatiens walleriana. The fungus seems to have become more deadly and persistent, and now many gardeners are forced to find alternatives to common impatiens.

For shady gardens and patios try New Guinea impatiens, which don’t fall prey to the fungus. The New Guinea impatiens (Impatiens hawkeri) has larger flowers than common impatiens. They grow about 12 to 24 inches tall. New Guinea impatiens are tropical, only hardy to USDA zones 10 and 11, so will die if left outdoors in the winter, but do well indoors as a potted plant.

Try New Guinea impatiens in hanging baskets, pots and window boxes. In the garden they do well as edging plants or massed by the hundreds for a dramatic focal point in the shady garden.

Unlike the common impatiens, the New Guinea variety is hard to grow from seeds and is usually propagated from cuttings. Choose healthy four-inch- long pieces of stem and put them in water where they will root within weeks.

In the garden center, choose New Guinea impatiens plants that are stout, well-branched with shiny, healthy leaves and lots of flower buds. Avoid spindly or leggy plants.

New Guinea impatiens like to be a little pot-bound, so wait until the roots fill the pot before moving to the next larger size. When it is time to repot your New Guinea impatiens, choose a pot about one and-one-half the diameter of the root ball. Pot them up in light potting soil that contains peat moss or vermiculite and perlite for drainage.

When setting New Guinea impatiens outdoors, add lots of compost or peat moss so the soil drains well.

New Guinea impatiens do best with afternoon shade. In hot sun the leaves can scorch and the plant will suffer. Keep them well watered but not soggy. Potted plants dry out much quicker than plants in the ground, so keep an eye on them during the hottest days of summer. Once a month, fertilize them with a good organic fertilizer that is low in nitrogen. Keep the flowers coming by removing flowers as they fade, a process called deadheading.

Switch from the common impatiens (Impatiens walleriana) to the New Guinea impatiens (Impatiens hawkeri) and you will have the same shade-loving flowers that are easy to grow with few troubles. If only all loves could be so simple.

  • Paul Barbano writes about gardening from his home in Rehoboth Beach. Contact him by writing to P. O. Box 213, Lewes, DE 19958.

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