Impatiens, a shade garden workhorse, goes lame

July 30, 2024

Impatiens are cheerful, mounded annuals that provide precious and steady floral display in shadier corners of the patio and border and look great in containers. But they are so good, folks with sun-robbed yards don’t think to plant much else. This year, they might have to.

A widespread and devastating disease, impatiens downy mildew, escaped the controlled environment of the growers' greenhouse two years ago and has spread virulently in the gardens and commercial and institutional landscapes in 35 states and the District.

The official advice is that if your impatiens melted and died abruptly last year, skip them for this growing season. Even if they didn’t, planting them will be a big risk as humid and moist conditions — read, the Washington summer — will promote the downy mildew in the months ahead.

Finding them might also be tough: The disease is so devastating that some nurseries are not selling them in 2013 and major growers have cut back impatiens production drastically.

This is a big deal in the flower trade. In the past 50 years impatiens have become one of the major bedding annuals by volume and dollar value as breeders figured out how to grow impatiens that were bushier and had more flower punch.

Homeowners and commercial landscapers developed a large appetite for them.

"It's one of our most popular annuals, second for us only to petunias," said Gary Mangum, whose company in Elkridge, Bell Nursery, supplies Home Depot retailers in much of the Mid-Atlantic. His growers have reduced impatiens production by more than 50 percent this spring.

Meadows Farms, a major garden center retailer with 22 locations in the region, announced it was not selling disease-prone impatiens this year. Usually, the plant represents 30 percent of its sales in annuals.

“People don’t understand the extent of the problem,” said Barry Perlow, a designer at Meadow Farms Landscaping in Chantilly. “By planting them now, they’ll be compounding the problem. The spores live for years.”

Actually, even if everyone were to stop growing impatiens — an unlikely scenario — a moratorium might do little to block the disease, said Margery Daughtrey, a plant pathologist at Cornell University, because its spores appear to survive on other host plants. One of them is the native jewelweed, that rangy, orange-flowered wildflower found along streambanks and noted for its coiled, explosive seed capsules.

Daughtrey said the golden age of the impatiens may be over.

“Long-term, I think we’ll see impatiens being a minor bedding plant instead of a major bedding plant,” she said. “This is something that has changed it from a plant with almost no diseases or insect problems to a plant with a real Achilles’ heel.”

The long-term solution might be for hybridizers to breed resistant strains but "we are a long way from getting resistant ... varieties," said Mary Ann Hansen, a plant pathologist at Virginia Tech. "We need to learn a different approach, not planting those large beds of a monoculture."

The fungal disease, which surfaced in Europe a decade ago, showed up in commercial greenhouses in the United States soon after, but was controlled by fungicides unavailable to consumers. The disease appeared in gardens in New York in 2009 and by 2011 it was widespread, discovered in California, the Midwest, Florida and the Northeast. It hit our region last year.

The disease affects common garden impatiens, hybrids of a species called Impatiens walleriana. The more sun-tolerant New Guinea impatiens are bred from a different species and are tolerant to the disease.

In the early stages, the leaves begin to curl and develop a yellow cast. This often leads to a white fuzz on the underside of leaves — hence “downy” — followed by leaf and flower drop and, finally, a collapse of the fleshy stems.

“The spores of the fungus can survive [the winter] in the soil and can survive on some weed hosts,” said Adria Bordas, horticultural extension agent for Fairfax County. She advised against planting impatiens where you grew them last year, especially if they succumbed to the downy mildew.

The spores travel in the air for miles and spread between plants in water on leaves, from rain or irrigation systems.

The diseased plants on one property, unless they are pulled and bagged right away, are likely to infect neighboring impatients, Daughtrey said. The early presence of the disease takes some sleuthing: You have to turn up the underside of the leaf to detect the downy affect, which may be slight. Three or four weeks later, the plants may denude abruptly, causing homeowners to think chipmunks or deer are the problem, she said.

“If you haven’t seen the disease before, you have a chance of being able to grow impatiens that are healthy,” she said. That will depend on buying disease-free plants, the weather “and whether your neighbor’s plants are healthy.”

I would avoid common garden impatiens this year, and this abstinence will have its own reward: It forces the shade gardener to try different plants. You might not attain the same simple floral show, but you can achieve more interesting effects with foliage and leaf colors.

Apart from the New Guinea impatiens, Mangum suggests the common wax begonia or the showier Whopper variety or, my favorite, Dragon Wing.

Some dazzling varieties of caladiums and coleus have been introduced in recent years, both of which grow steadily and heartily through the warm months until becoming preening beasts in September. Bell Nursery has launched a line of alternatives called Shady Shakeupin smaller sizes to allow the same sort of mass planting desired with impatiens. Small sizes soon bulk up in the warmth of May, given rich soil, adequate moisture and a weekly feed of diluted fertilizer.

Another silver lining: What if we dump the ring of impatiens around the old oak tree and plant some perennials in considered compositions that rely more on foliage textures and colors than flowers alone? You could assemble such beauties as hostas, coral bells, creeping phlox, gingers, hakone grass, sedges and ferns, particularly the Japanese painted fern. Once planted with adequate space and a measure of patience, they will not need replanting each year.

Impatiens alternatives

Here are other shade-loving annuals for a season of ornament and bloom.

New Guinea impatiens: Developed for sunny locations but happy in partial shade, New Guinea impatiens are larger than common garden impatiens, with fewer flowers but striking leaf forms and variegation.

Petunias: Advances in petunias have produced self-cleaning, continuous-blooming hybrids. Happy in partial shade.

Begonias: Wax begonias offer a blend of leaf and flower ornament. Other begonias are grown more for their attractive foliage. Look for Whopper, Dragon Wing and Gryphon, the last a black-and-silver-leaf foliage plant. All work well in containers.

Coleus: Grown for their leaf coloration and markings, coleus are as stunning as they are varied.

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