“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.
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.