Impatiens in Canada
The shade annual everyone grew, the disease that changed it, and what to plant now.
Impatiens in Canada were the default shade annual for decades. The University of Wisconsin–Madison Extension explains what changed: impatiens downy mildew, a disease so destructive it made garden impatiens unusable as an ornamental in places.
Garden impatiens are tender. NC State rates Impatiens walleriana hardy only in US Zones 10 and 11, so in Canada they are planted out after the last frost and treated as annuals.
Impatiens at a glance: Plant after your last frost in partial or deep shade. Garden impatiens can be wiped out by impatiens downy mildew; New Guinea impatiens and the downy-mildew-bred Beacon and Imara XDR series resist it. If plants show white fuzz under the leaves, remove and bag them; do not compost.
Want another shade bloomer? See Growing Fuchsia in Canada for shade baskets.
Spotting Downy Mildew
The University of Wisconsin describes the signs: yellow-green leaves, often near the branch tips, that curl downward; stunting and fewer flowers; then leaves and flowers dropping to leave bare stems. The giveaway is white, fuzzy growth on the undersides of the leaves. Cool, wet or humid weather favours it.
What to Do If You See It
The same source says infected plants are unlikely to recover. Remove them, roots and all, seal them in plastic bags and put them in the garbage, not the compost. Consider removing impatiens within about a metre (three feet) as well. Fungicides on plants already showing symptoms are not effective.
What to Plant Instead
| Option | Downy mildew |
|---|---|
| New Guinea impatiens and hybrids (e.g. SunPatiens) | Resistant or tolerant |
| Beacon and Imara XDR garden impatiens | Bred for resistance |
| Begonia, coleus, torenia, alternanthera, iresine | Not affected |
From the University of Wisconsin. It notes even resistant varieties can develop the disease in bad conditions, and recommends mixing several kinds of bedding plants. See tuberous begonias.
Buying and Planting
The University of Wisconsin advises inspecting plants before buying, then holding new plants apart for 5 to 14 days to watch for symptoms before planting. NC State lists garden impatiens for dappled, partial and deep shade. Plant after the last frost; see last frost dates.
Frequently Asked Questions
Why did my impatiens suddenly collapse?
Often impatiens downy mildew. Look for white, fuzzy growth under the leaves and leaves dropping to bare stems.
Are New Guinea impatiens resistant to downy mildew?
The University of Wisconsin says New Guinea impatiens and their hybrids appear resistant or tolerant.
Which garden impatiens resist downy mildew?
The Beacon and Imara XDR series were bred for resistance, according to the University of Wisconsin.
What should I do with impatiens that have downy mildew?
Remove them roots and all, seal them in plastic bags and put them in the garbage. Do not compost them.
When can I plant impatiens outside?
After your last spring frost. NC State rates them hardy only in US Zones 10 and 11.
What can I plant instead of impatiens in shade?
The University of Wisconsin suggests begonia, coleus, torenia, alternanthera and iresine, which are not affected.
Sources
- University of Wisconsin–Madison Extension — Impatiens Downy Mildew
- North Carolina State University Extension Gardener Plant Toolbox — Impatiens walleriana
- North Carolina State University Extension Gardener Plant Toolbox — Impatiens hawkeri (New Guinea impatiens)