Impatiens

The disease that changed which impatiens you can buy

Impatiens were the default shade bedding plant in America for decades. Then downy mildew arrived and reset the whole category, and anyone buying them now needs to know which plant is in the tray.

NC State names the organism: Plasmopara obducens, and adds the detail that matters most. Fungicides used to control fungal diseases will not work on downy mildew, because it is a fungus-like organism rather than a fungus.

It behaves brutally. Leaves yellow and drop, the plant defoliates within days, and a bed that looked full on Friday is bare stems by the following week. The spores persist in soil, so a bed that has had it is a bad bet the following year.

The practical answer is species rather than treatment. NC State records Impatiens hawkeri, New Guinea impatiens, as resistant to downy mildew. In a garden that has lost impatiens before, that is the plant to buy.

The part of the story that is more recent

Switching species is no longer the only answer, and this is the piece most older advice is missing. Breeders spent years selecting Impatiens walleriana itself for resistance, and two seed series reached the American market in 2019 and 2020.

• Imara XDR, from Syngenta. The XDR stands for extra disease resistance, and the claim was verified by independent plant pathologists at Cornell rather than by the breeder alone.
• Beacon, from PanAmerican Seed, released to selected nurseries in 2019 and to the wider market in 2020.

Michigan State grew a number of the resistant varieties in its 2019 trial garden and reported them holding through the whole summer without developing the disease, and a landscape study the same year found Imara XDR significantly less susceptible than the older types.

Two qualifications keep this honest. Resistant is not immune, and the spores still persist in soil, so a bed that has had a serious outbreak is still a poor place to replant. And the resistance belongs to the named series, not to impatiens in general: an unlabeled tray of bedding impatiens is as vulnerable as it ever was. Buy by series name.

Types of impatiens, and which one suits the site

What is sold as impatiens now covers three quite different plants, and the differences that matter are sun tolerance, size and disease resistance rather than flower color.

New Guinea types are told apart on the leaf as much as the flower: larger, narrower foliage in bronze or purple tints, sometimes variegated, with the underside often red or purple, and a long spur behind each flower. Next to a tray of common impatiens the difference is obvious once you have seen it.

Are impatiens full sun plants?

It depends entirely on which of the three you have, and this is the question behind most disappointed impatiens.

• Common impatiens: no. Part to full shade. NC State allows that it may manage a partly sunny spot given enough water, but too much sun scorches the leaves. This is a shade plant and its whole value is flowering where little else does.
• New Guinea impatiens: yes, with water. It adapts across the full range from deep shade to full sun, and the trade is stated plainly in the extension record: the more sun it gets, the more water it takes. In a hot climate that can mean daily watering in a container.
• SunPatiens: yes, by design. These are the interspecific hybrids bred specifically for sun, and Penn State trial reports have them holding color and form through heat, humidity and irregular summer rain across the compact and vigorous series alike.

If a plant labeled only impatiens is wilting flat by midday in a sunny bed, the label is the problem rather than the care.

What it wants

Part shade to full shade. NC State notes it may grow in partly sunny areas with adequate water, but too much sun scorches the leaves.

That shade tolerance is the whole reason for the plant’s popularity: it flowers continuously from late spring through early autumn, May to October, in a position where most bedding plants sulk.

Soil should be moist, well drained and high in organic matter, at a slightly acidic pH. Size is 0.5 to 2 feet tall and about as wide, spaced anywhere from under a foot to three feet depending on use.

Hardy only in zones 10a to 11b, so almost everywhere it is grown as an annual.

Growing it

1. Water before it wilts, not after

   Impatiens collapse dramatically when dry and recover from it, but repeated wilting costs flowers and invites problems. This is a plant with a genuinely high water demand.

2. Space it properly

   Crowded plants hold still humid air between them, which is what both mildews want. Spacing is a disease measure here, not a tidiness one.

3. Water the soil, in the morning

   Foliage that stays wet overnight is the condition downy mildew needs to establish.

4. Do not replant the same bed after an outbreak

   The spores persist in soil. Move to containers with fresh compost, or switch to New Guinea types.

5. Feed lightly and regularly

   Continuous flowering for five months is a real demand, and container plants exhaust their compost by midsummer.

Where it works, and what the blooms look like

The flowers are white, peach, apricot, pink and red, single or double, each with a conspicuous white elongated spur behind it, and they carry from late spring until the first frost. White is worth singling out: in a shaded bed it reads at a distance in a way the darker colors do not, which is why white impatiens are the standard choice for lighting a dim corner.

The uses follow from the mounding habit and the shade tolerance. NC State lists containers, hanging baskets and planters, edging along a shady border, mass planting in a woodland setting, and defining a walkway. A hanging basket suits the plant particularly well, since the mound spills over the rim and the raised position gives it the air movement that beds at ground level often lack.

The one caution on baskets is water. A hanging basket dries faster than anything else in the garden, and this is a plant with a high water demand that wilts flat when it runs short. In summer that usually means checking it daily rather than on a schedule.

Spacing, containers and seed

Three practical points that the general advice above leaves open, and spacing is the one that does double duty as both a planting decision and a disease measure.

• Spacing. Clemson gives 18 inches apart for tall-growing varieties and 8 to 10 inches for compact ones. Closer than that and the still humid air between the plants is what both mildews want, so the wider figure is the safer one on any site that has had trouble.
• Containers. The plant suits pots well and asks more of you in them: more frequent watering, and more feeding, since five months of continuous flowering exhausts a container mix by midsummer. A water-soluble fertilizer monthly is the usual recommendation. Containers with fresh mix are also the way to keep growing common impatiens on a site where the soil is contaminated with downy mildew spores.
• No deadheading and no pinching. Impatiens are self-cleaning, dropping their spent flowers themselves, and they build a good shape without being pinched. This is one of the few bedding plants where doing nothing is correct.

From seed, start common impatiens indoors six to 10 weeks before they go outside, which is a long lead and the reason most people buy transplants instead. New Guinea impatiens are usually grown from cuttings rather than seed in the trade; from seed they want soil held at 70 to 75°F to germinate.

Seed saved from a garden plant is worth a caution. Modern impatiens are hybrids, so seedlings do not come true, and seed collected from a resistant series does not carry the resistance reliably. If disease resistance is the reason for the choice, buy fresh plants or fresh seed of the named series each year.

What else goes wrong

NC State lists aphids, spider mites, slugs and snails among insects, and powdery mildew, downy mildew and verticillium wilt among diseases, with deer browsing described as problematic.

Slugs are worth naming separately. A soft, shade-grown, constantly damp plant is exactly what they want, and a newly planted bed can be stripped in a night.

Deer eat impatiens readily. In deer country this is not a plant for an unprotected bed.

Telling the two mildews apart matters because only one is a catastrophe. Powdery mildew is a white dusting on the upper leaf surface and is cosmetic. Downy mildew shows as yellowing leaves with a fine white or gray coating on the underside, followed by rapid leaf drop, and it ends the planting.

Toxicity, in plain terms

NC State lists Impatiens walleriana as non-toxic to cats, dogs and horses. That is a positive statement of safety rather than an absent listing, which makes it a reasonable choice for a shaded bed in a garden with animals.

Frequently asked questions

Why did my impatiens collapse and drop all their leaves?

Almost certainly downy mildew. Leaves yellow, a fine coating appears on the undersides and the plant defoliates within days. NC State notes ordinary fungicides do not work on it, because the organism is not a fungus.

Can I plant impatiens in the same bed again?

Not after an outbreak. The spores persist in the soil. Use containers with fresh compost, or switch to New Guinea impatiens, which NC State records as resistant.

How much sun can they take?

Part shade to full shade. They can manage partly sunny spots given enough water, but too much sun scorches the leaves. Shade tolerance with continuous flowering is the reason to grow them at all.

Why do mine wilt every afternoon?

High water demand plus too much sun or too little root room. They recover from wilting but repeated collapse costs flowers. Water before it happens rather than in response to it.

Are impatiens safe around pets?

Yes. NC State lists them as non-toxic to cats, dogs and horses. Deer, on the other hand, eat them readily, which is a different problem entirely.

Companion plants