New Guinea impatiens is the go-to plant for gardeners who would like to continue to have impatiens in their yards, because impatiens downy mildew does not affect New Guinea impatiens.
Photo courtesy of MetroCreative Connection
A: You are referring to Plasmopara obducens, a pathogen that is extremely aggressive and generally known as impatiens downy mildew. It begins with spotting or stippling of the leaves, curling of leaves in a downward fashion and leaf yellowing. A white, fuzzy growth develops on the underside of both yellow leaves and healthy green leaves. Eventually the leaves drop from the plant leaving bare stems behind. In the past few years, this disease has become increasingly widespread in North America. It is pretty much here to stay, but will vary in intensity depending on a particular year’s weather patterns.
In general, the disease is spread by two different types of spores. One type is airborne and remains viable for just a short time. The other type moves through a film of water.
It develops in cold or warm weather when plant foliage remains wet for prolonged periods and relative humidity is high.
Fungicide sprays or washes are of little help to the home gardener. To control impatiens downy mildew, water only in the mornings, and only on the surface of the soil; do not wet the foliage.
For folks who are nostalgic about having the same type of impatiens in their summer gardens as always, if you spot downy mildew on your impatiens, remove and dispose of the entire infected plant, including roots, immediately. Toss it in the trash, not on the compost pile. Do not replant the infected area with more of the same impatiens.
New Guinea impatiens is the go-to plant for folks willing to have a close relative of impatiens in their yard, because impatiens downy mildew does not affect New Guinea impatiens — or other flower or vegetable plants for that matter.
The blossoms of New Guinea impatiens are extra large and can provide brilliant color in somewhat sunny spots, as well as in shade. Depending on the cultivar you choose for your garden, New Guinea impatiens have foliage colors that range from solid dark green to innumerable variegated choices.
Here is a partial list of New Guinea impatiens cultivars and hybrids to choose among:
√ ‘Applause Orange Blaze’
√ ‘Celebration Blush Pink,’ ‘Celebration Bright Salmon,’ ‘Celebration Lavender Glow,’ ‘Celebration Orange’ and ‘Celebration Raspberry Rose’
√ ‘Celebrette Deep Red,’ ‘Celebrette Hot Pink,’ ‘Celebrette Orchid Star’ and ‘Celebrette Purple Stripe’
√ Fiesta™ ‘Appleblossom’ and Fiesta™ ‘Burgundy Rose Double’
√ ‘Infinity Cherry Red’ and ‘Infinity Lavender’
√ ‘Painted Paradise Lilac,’ ‘Painted Paradise Pink,’ ‘Painted Paradise Red’ and ‘Painted Paradise White’
√ ‘Paradise Cherry Rose,’ ‘Paradise Lavender on Fuchsia,’ ‘Paradise Mango Orange,’ ‘Paradise Rose on Violet’ and ‘Paradise Salmon Pink’
√ ‘Sonic Magic Pink’
All impatiens require a good, well-drained soil, adequate moisture and afternoon shade. New Guinea impatiens grow best with about four to six hours of afternoon shade and prefer soil that is consistently moist but not soggy. Choose plants that are mounded and well-branched with healthy root systems, shiny leaves and lots of flower buds. Plant them immediately if you can; don’t let them dry out. And don’t store the plants in a dark, dry location. Provide bright light but no direct sun.
Loosen the soil and mix in compost or peat moss, along with an all purpose fertilizer. Top-dress the soil bed with slow-release fertilizer. Set the plant into the soil at the same level it grew in its pot. Water at ground level to avoid wetting the foliage.
For other annuals to plant in shade that are not toxic to dogs, consider violets, begonias, coleus, nasturtium, primrose and spider flower (Cleome hassleriana).
For a comprehensive list of plants that are dog friendly, visit dogsinthegarden.com/plants-friendly.html or www.aspca.org/pet-care/animal-poison-control/dogs-plant-list.
Q: Is it too late to cut back my roses?
A: I sure hope not, because I have yet to assess the winter damage to my own rose bushes and then act accordingly. A preliminary stroll-by tells me that most of the canes will require aggressive pruning, some nearly to the ground. Always prune dead or diseased canes as soon as you find them. Prune canes with blackened, dead wood back until you reach a healthy part of the cane with a white center.
If you wish to cut back your roses to shape them, keep in mind that some roses, such as ramblers and some climbers, bloom only once per year. They can be pruned as soon as the flowers fade. Rebloomers can be pruned in early spring to shape the plant and promote air circulation.
For more horticultural information, call the OSU Summit County Hotline Tuesdays between 9 a.m. and noon at 330-928-4769, ext. 3. Request Fact Sheet HYG-1205-96, Fertilizing, Pruning and Winterizing Roses.
Please note fact sheets are sent out free, but there is a fee for bulletins. Many bulletins are available online at ohio line.osu.edu and can be printed from home or accessed at the public library.
Dayle Davis is a freelance writer and avid perennial gardener, with a B.A. in communications and coursework in botany, geology and wildflowers. Davis is certified as a Master Gardener under The Ohio State University’s Horticultural Extension. Readers can send in questions regarding lawn and garden issues, which could be featured in a future edition. Questions can be emailed to firstname.lastname@example.org, faxed to 330-665-9595 or sent to Leader Publications, 3075 Smith Road, Suite 204, Akron, OH 44333. Please do not send any leaves, seeds or other organic material.
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