Q. Is it safe to plant impatiens this year? If not, what can I plant to replace the diseased impatiens?
Impatiens downy mildew, caused by the pathogen Plasmopara obducens, first became widespread in our area in 2011. It has caused severe defoliation and flower drop of impatiens. Unfortunately, this blight is not going away. All varieties of Impatiens walleriana, the traditional bedding plant, are highly susceptible to this disease. The pathogen's spores spread easily via wind and water and can remain in soil over the winter. Infected plants do not recover and have to be removed. So it is not safe to plant any I. walleriana.
Balsam impatiens, I. balsamina, is also susceptible, although damage is usually limited to yellow spots on leaves.
Fortunately, New Guinea impatiens, I. hawkeri, is immune to impatiens downy mildew. New Guinea impatiens plants are larger than I. walleriana, with larger flowers. They grow best in partial to total shade. A hybrid variety, I. hybrida Bounce™, is particularly robust. With this sturdier plant, you can still have impatiens in your summer shade garden.
For bright, sunny areas, there is the I. hawkeri SunPatiens® series, the first impatiens developed to flourish in full sun. These plants are generally larger and bushier than other New Guinea impatiens, and produce more flowers.
Many other bedding plants can also be planted in place of impatiens. See Cornell Cooperative Extension Suffolk County's Alternatives to Garden Impatiens for a list of potential substitutes, with information on each.
The extension also provides factsheets on impatiens downy mildew and other common plant blights.
Also see the University of Minnesota's Managing Impatiens Downy Mildew in the Landscape.
For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service