Last fall a reader alerted me to the fungal disease that has devastated that wonderful shade annual, impatiens, throughout much of New England. The disease, called impatiens downy mildew, will be a problem again for most gardeners this year. Any garden that had the disease last year will have it again this year -- even our coldest winters will not cleanse the soil of it. I wish I had known about it sooner, as prompt removal of affected plants may stop the spread of the disease. So if you did not have the disease last year, watch your plants carefully this year and bag and dispose of any diseased plants promptly.
Impatiens downy mildew symptoms are these: Yellowing of leaves, then a limp appearance, as if it needs to be watered. Next comes a downy white fungal growth on the undersides of leaves. Then leaves and flowers drop, leaving just a stem with a few leaves on top -- as if slugs had eaten the leaves. I have read that if you don’t plant impatiens in a site that has had the disease for a year or two, the soil may become free of disease. But I wouldn’t count on it.
There are two related plants that will thrive in shade or part shade and that are not susceptible to the mildew: New Guinea impatiens and SunPatiens, which is a trademarked hybrid. SunPatiens is advertised as good for part sun to sun -- but not deep shade. But it is being marketed as a replacement of impatiens. I wonder if it will be able to bloom as vigorously as our old favorite in full shade. Both are generally sold in individual pots for around $5, quite an upgrade from a six-pack for $3.50 or so that I was accustomed to paying for impatiens in past years.
Another plant that is being touted as a replacement for impatiens is Torenia. I spoke to two landscapers who have used Torenia in past years and say that it is nice enough, but it will not satisfy impatiens-lovers. I’ve heard that it does not have as many blossoms per plant, generally, and is often available in just a few colors -- shades of blue and purple, and in white. However, I have found it for sale in multi-packs in a few places and did find one nursery with four-packs that listed rose, magenta, lemon drops and white as colors available.
I have used bedding lobelia as a nice shade annual, though in my experience it wants a little sun or filtered sun. I love the intense blue that it often displays, though it is available in other colors, too. I started seeds indoors back on April 17, a mix called ‘Cascade of Color’ that promised blue, blue with a white eye, lilac, red, ruby and white.
Right now my lobelia seedlings are only two inches tall but I assume they will take right off when I separate them and get them in the ground. The only problem with a mix like that is that one cannot determine what color any given seedling will be -- unless you wait for them to bloom in the pot. And, when I read the seed packet (from Botanical Interests) just now, I see that this variety is advertised for full sun. I have plenty, so I’ll try some in shade, too.
So what else can we do to provide color in shade? Try some perennials. Granted, most only bloom for one to three weeks, but if you select plants with good foliage they can be a joy all summer. I love European wild ginger (Asarum europaeum) for its very glossy dark green leaves. It forms a nice expanding clump, even in dry shade with competition from tree roots. The blossoms are hidden beneath the foliage, but it doesn’t matter to me. This is a great shade plant. I plant them in clumps of three about 18 inches from center to center.
Then there is bigroot geranium (Geranium macrorhizum). Not to be confused with your mom’s red geraniums (which are technically not geraniums at all), this is a nice spreading plant that thrives in full shade and blooms with pink, magenta or white flowers in late May or early June. The leaves look good all summer, each plant a spreading mound 12 to 18 inches tall and 15 inches wide. I use it as a groundcover. I have read that it will do well in sun, too, and that it tolerates a wide range of soil and pH conditions. If it wanders too far? It pulls easily, and you can give the roots to someone who doesn’t have it.
I have never tried either the geranium or the ginger in a pot, but will this year and grow them on my north-facing, shady deck. I’ll give them a 50/50 mix of standard potting soil and compost, and I bet they look just fine.
It seems that every year there is a new bug or a new disease that threatens some plant in our garden. I guess we will have to keep on adapting and changing -- just like the pests do. Good luck!
Henry Homeyer is the author of four gardening books and a children’s fantasy-adventure called Wobar and the Quest for the Magic Calumet. You may reach him at PO Box 364, Cornish Flat, NH 03746 or firstname.lastname@example.org.