Impatiens (Impatiens walleriana), an annual flower, is common in partial shade gardens. Unfortunately for us home landscapers, impatiens may not be available because of a widespread breakout of downy mildew, a disease that attacks plant foliage. There have been "sporadic reports of impatiens downy mildew in U.S. greenhouses since 2004," reports Ball Horticultural Company in their article, "ImpatiensDowny Mildew: Guidelines for Growers." The article goes on to say, "By the end of the 2012 season, impatiens downy mildew had been confirmed in 33 states." Downy mildew causes yellowing of leaves and stems that leads to dieback of the plant. Downy mildew is spread by spores, meaning that healthy plants could contract the diseases from neighboring affected plants. Since impatiens are not available to purchase this year, I researched other annual flowering plant options for partially shady areas.
New Guinea impatiens
New Guinea impatiens (Impatiens x New Guines Hybrids) is similar to Impatiens walleriana but with larger leaves and is resistant to downy mildew. New Guinea impatiens grows 6 to 24 inches tall in partial sun to partial shade. Blooms may be pink, purple, red, orange, lavender, or white. Picture of Dorne.
Browallia (Browallia speciosa), also known as amethyst flower and bush violet, grows 1 to 2 feet tall and in partial to full shade. Blooms, which appear for a few weeks in the summer, may be bluish purple or white. Browallia works well in indoor or outdoor planters.
Wax begonia (Begonia x semperflorens-cultorum) grows 6 to 18 inches tall in partial sun to partial shade. The leaves of wax begonia are large and shiny. Blooms may be pink, red, or white. If desired, dig up the plant before the first frost to take indoors. Cut the plant back about one-third and place potted begonia by a sunny window. Plants may be returned outdoors in the spring. Picture courtesy of Wildfeuer.
Wishbone flower (Torenia fournieri) displays blooms in shades of blue, purple, yellow, or white from summer into fall. Wishbone flower grows about 12 inches tall. Plant in partial shade.
Sweet alyssum (Lobularia maritima) is my favorite and for a reason others may find unsatisfactory—sweet alyssum self-seeds liberally. Seeds blow to land in areas where you may not want the plant. Despite that, sweet alyssum offers scented tiny blooms of white from mid-spring to the first frost. Sweet alyssum grows 8 to 12 inches tall in partial shade to full sun.