Impatiens, the busy Lizzie of window boxes, is a tender annual grown for continuous bloom in shade and part shade, where few flowering plants perform. The flat, five-petalled flowers in white, pink, red, orange, lavender and bicolours cover plants 6 to 18 inches tall from late spring until frost, and the plant branches and reblooms with no deadheading. It is native to eastern Africa and is grown as a warm-season annual everywhere in the US.
Set plants out after the last frost, once nights stay above 50°F, 8 to 12 inches apart in rich, moist soil in shade or morning sun; it wilts in hot afternoon sun. It needs consistent moisture and wilts fast when dry, though it usually recovers after a drink. Feed lightly every few weeks in containers. Pinch leggy plants back by half in midsummer and they fill in within two weeks.
Impatiens downy mildew has caused widespread losses since the 2010s: yellowing leaves, white fuzz beneath, then bare stems. Where it is established, grow the resistant Beacon and Imara series, or switch to New Guinea impatiens or SunPatiens, which are immune. Slugs are the other pest. Hummingbirds visit the flowers. Deer and rabbits graze it, so it belongs in containers or a fenced bed where they roam.
Impatiens Downy Mildew
Leaves yellow, curl downward, and drop, leaving bare stems. A white, fuzzy coating forms on leaf undersides. Plants may collapse quickly in cool, wet conditions.
No effective home cure once infected. Remove and bag all infected plants, including roots; do not compost. Avoid overhead watering and crowding. Replant resistant impatiens varieties (such as Impatiens hawkeri) or other shade plants, and rotate away from the area, as spores persist in soil.
Botrytis (grey mould)
Grey fuzzy mould on petals and stems, worst in cool wet conditions.
Remove affected parts immediately. Improve air circulation. Avoid overhead watering. Apply copper fungicide if severe.
Spider Mites
Tetranychus urticae →Fine stippling or bronzing on leaves, faint webbing on undersides, foliage drying out during hot, dry weather.
Spray foliage with a strong jet of water to dislodge mites. Apply insecticidal soap or horticultural oil to leaf undersides; repeat every 5–7 days as needed.
Aphids
Aphididae →Clusters of small soft insects on new growth and flower buds.
Knock off with a strong jet of water. Ladybirds and lacewings are natural predators. Insecticidal soap as last resort.