What’s the current status about planting impatiens in the Garden in Toronto ( Zone 7)? Many varieties were hit by a virus and would frizzle after panting them. Are they free from the virus now? Can I bring them indoors at the end of the summer? Will they survive? Thank you.
Over the last several years across North America, an outbreak of downy mildew (caused by Plasmopara obducens) attacked common impatiens (Impatiens walleriana). It also afflicts other impatiens varieties – rose balsam (I. balsamina), native wild impatiens (I. pallida) and jewelweed (I. capensis). The pathogen can survive in soils for 10 years or more and once a plant is infected, that plant and those surrounding it must be destroyed and discarded in the garbage (in bags, so that the spores do not spread). Downy mildew is a particular risk in conditions of high humidity, cool temperatures and where plants are crowded together, leaving little room for air circulation.
Note that downy mildew is not a virus. There are viruses like the impatiens necrotic spot virus that attacks not only impatiens, but many other host species. However, it was the downy mildew that was responsible for the downfall of the common impatiens a few years ago – resulting in these plants being pulled from the market. New impatiens varieties are available that are more resistant to downy mildew. These are discussed below.
New Guinea impatiens (Impatiens hawkeri) are considered resistant to the downy mildew. Besides this variety, hybrids that are a result of crossing I. hawkeri with closely related species (e.g., I. platypetala, I. aurantiaca and others) are touted as resistant to downy mildew. SunPatiens® and Bounce® hybrids have been available for a few years. SunPatiens® was the first impatiens that would thrive in full sun, and also likes heat and high humidity. These plants result from a cross between I. hawkeri and wild impatiens. Bounce® is the result of a cross between I. hawkeri and I. flaccida.
There are a couple of newer and promising Impatiens walleriana promoted as having “high resistance” to downy mildew – Beacon® and Imara XDR® [XDR means extra disease resistant]. I scoured the internet to check if nurseries sell these plants, but found nothing. This may be because most literature indicated that the brands were to be launched in 2020. However, both brands are available on-line via seed catalogues. For a helpful update on this issue, see Winnipeg Free Press. The fall and return of impatiens. This article is from several months ago, but is the most current I located.
If you prefer to wait a couple of seasons to assess how “high resistance” Impatiens walleriana actually perform in the garden, Cornell Cooperative Extension’s Alternatives to garden impatiens provides many great suggestions.
Finally, if you wish to overwinter a few plants indoors, cut them back, and bring them inside before temperatures are in the 4 degree C (40 degree F) range. Place in full sun, and water regularly. Alternatively you can take stem cuttings from an outdoor plant and root these. Impatiens may be challenging to grow as houseplants, as they are demanding – they need lots of light and soil that is rich and drains well. Don’t fertilize the plants until the days get longer in late March or so. If you will be putting the plants outdoors the following summer, once all danger of frost has passed, start acclimating the plants to the outdoors. See SF Gate. Can you bring impatiens inside?