Impatiens have traditionally been one of the most popular bedding plants in the United States because of their beauty and ease to grow. Few annuals that grow in shade provide the range or intensity of color as impatiens. Unfortunately, particular species of impatiens are susceptible to the disease impatiens downy mildew caused by a water mold, Plasmopara obducens.
Compact impatiens grow 10 to 16 inches tall and approximately 10 to 15 inches wide. Newer varieties of impatiens grow to heights reaching up to 36 inches.
The wide range of flower colors includes red, orange, salmon, rose, pink, white, violet, and lavender blue. New Guinea Impatiens also offer exciting variations in leaf color.
Impatiens are tender annuals throughout South Carolina. They work well for edging shady beds, mass plantings under trees, window boxes, and hanging baskets.
Many older types of impatiens thrive in filtered or partial shade and must have protection from hot afternoon sun to maintain their colors. The soft, fleshy stems wilt quickly when in need of water. Newer varieties of impatiens tolerate heat allowing them to grow in much more sunny locations. Plants grown in soil under trees will need extra water and fertilizer, since they are competing with tree roots.
All types of impatiens do best in a rich, moist soil mulched to maintain adequate moisture. Fertilize monthly with a water-soluble fertilizer.
Impatiens are easy-care annuals that develop a beautiful shape without pinching or pruning. In addition, impatiens are self-cleaning, so removal of spent flowers is not required.
Start impatiens seed indoors six to 10 weeks prior to planting outside. After the last chance of frost, harden off impatiens seedlings, and then set the plants in the garden. A quicker way to get impatiens is to purchase transplants from a local nursery or garden center. Space tall-growing varieties 18 inches apart and compact varieties 8 to 10 inches apart. If planted too close together, plants become taller and leggier.
Impatiens grow well in containers. Use a soil-less growing mix with good drainage. Impatiens grown in containers need more frequent watering and possibly more fertilizing than those grown in the garden.
Impatiens are somewhat trouble-free in the home landscape when the more disease resistant varieties are grown. Impatiens tend to be susceptible to moisture stress. Plants allowed to wilt will drop leaves and flowers. Keep them well watered, but not soggy, at all times. Diseases including damping-off during germination, fungal blights and rots, and viruses can occur.
The once commonly grown species Impatiens walleriana, and its hybrids, appear less in the landscape because of issues with impatiens downy mildew. Other species of impatiens susceptible to this disease are I. balsamina (Balsam Impatiens) and the native impatiens, I. pallida and I. capensis (Jewelweed).
Downy mildew of impatiens typically presents itself in late summer. It often begins with young plants and new growth showing signs of yellowing or yellow and green leaf stippling followed by the downward curling of the leaf. As the fungus continues to grow, a white, downy growth becomes evident on the underside of the leaf. Blooms may begin to drop followed by the leaves. Bare stems remain behind. If left, stems will wither and die leaving bare patches.
Impatiens downy mildew thrives during moist, wet conditions. High humidity further encourages the disease. Cultural controls to reduce leaf wetness include good soil drainage, adequate plant spacing to promote proper air circulation, sanitation (removing diseased plants immediately), and watering below the plant rather than overhead. Drip irrigation or soaker hoses placed in flowerbeds allow for ground level watering and help maintain leaf dryness. There will be some limited control of downy mildew on impatiens with fungicides. Some fungicides for homeowners include potassium salts of phosphorous acid (Monterey Agri-Fos), mancozeb (Bonide Mancozeb or Southern Ag Dithane M-45), or azoxystrobin (Heritage).
Remove plants showing severe symptoms of impatiens downy mildew for off-site disposal. Do not place diseased plants in compost bins where compost will be used later in the landscape. The disease can remain in the ground for several years. Replant the site with another type of flowering plant depending on amount of light the location receives.
Alternative species and cultivars of impatiens are more tolerant to impatiens downy mildew, such as New Guinea impatiens and interspecific hybrid impatiens. On the down side, New Guinea impatiens may experience problems with spider mites, thrips, mealybugs, and aphids infestations.
Always grow plants under their optimum growing conditions to keep them as healthy as possible. This will reduce disease and insect problems in the future.
Species & Cultivars
Impatiens cultivars are usually sold as part of a series with similar growth characteristics and a wide range of color.
Old-Fashioned Impatiens: Old-fashioned Impatiens (Impatiens walleriana), also known as Impatiens, Sultana, Touch-me-not, and Busy Lizzie, is the traditional impatiens species. It has a mounding habit, long bloom, and incredible range of colors. The common name Touch-me-not was given because the slightest touch will cause the ripe, full seedpods to burst open and scatter seeds into the wind. Impatiens often reseed in the garden, but the seedlings will gradually revert to producing tall plants with a mix of colors unlike those originally planted.
Old-Fashioned Impatiens range in height from 8 inches to 2 feet tall, depending on the cultivar. Many cultivars will be taller than descriptions in catalogs in hot southern summers. Heat-tolerant cultivars will remain more compact. Flowers are from one to 2 inches across. Taller plants produce larger flowers. Flowers can be single, semi-double, or fully double blooms that look like miniature roses.
Old-Fashioned Impatiens series include:
- ‘Accent’ series are dwarf, large-flowering and have outstanding summer-long flowering in shade.
- ‘Blitz’ series has very large 2½-inch blooms on uniform compact plants. They are drought-and heat-tolerant.
- ‘Carousel’ series has the largest percentage of double blooms of any double impatiens. The compact, well-branched plants flower freely.
- Dazzler® series grows 9 to 11 inches tall, 13 to 15 inches wide in shade. They are compact plants with large blooms and enormous flower production. Ideal for containers.
- DeZire® series grows 8 to 10 inches tall, 12 to 14 inches wide in shade. They are versatile for in-ground use as well as containers and hanging baskets.
- Expo® series grows 12 to 16 inches tall and 12 to 14 inches in shade. They perform well across a wide range of conditions.
- Fiesta™ series grows 10 to 14 inches tall and 10 to 12 inches wide in shade or partial sun. Produce double blooms.
- Impreza® series grows 8 to 10 inches tall and 6 to 8 inches wide in shade. They have a compact form and lodge or open up in the middle less.
- Super Elfin® series grows 8 to 10 inches tall and 12 to 14 inches wide in shade. Known for abundant bloom and compact habit even in heat.
- Super Elfin® XP series grows 8 to 10 inches and 12 to 14 inches wide in shade. Known for compact habit and uniformity.
New Guineas: New Guinea Impatiens (Impatiens hawkeri) have leaves that are large and brightly colored bronze or purple with yellow or pink midribs. They have large showy flowers in various colors usually grown from cuttings.
New Guineas grow in partial to full sun. Unfortunately, they need so much water to do well in full sun that few gardeners can keep up. New Guineas grow best where they will receive morning sun and afternoon shade. An eastern exposure is ideal. Gardeners who can water the plants very frequently may want to try them in full sun.
New Guinea series include:
- Celebration series grows 10 to 16 inches tall and 10 to 16 inches wide in partial to full sun. Landscape uses include borders and containers.
- Celebrette series grows 8 to 10 inches tall and 10 to 12 inches wide in partial to full shade. It has a compact form that produces large blooms.
- Clockwork™ series grows 8 to 10 inches tall and 10 to 12 inches wide in shade to partial sun. They have uniform habit of growth.
- Devine™ series grows 10 to 14 inches tall and 12 to 14 inches wide in partial sun. Foliage ranges from green to green-bronze.
- Harmony® series grows 10 to 18 inches tall and 10 to 18 inches wide in partial to full sun. They bloom early and consistently until fall.
- Magnum series grows 12 to 18 inches tall and 12 to 24 inches tall in partial to full sun. Suited for border, mass planting, and containers.
- SunStanding™ series grows 36 inches tall and wide in shade or sun.
Several exceptional New Guinea cultivars include:
- ‘Celebration Candy Pink’ is a light pink
bicolored variety with dark green foliage.
- ‘Celebration Light Lavender’ is a lavender variety with green variegated foliage.
- ‘Nebulus’ is an excellent selection with salmon-flowers and green foliage.
- ‘Equinox’ is a good selection for light pink flowers. It has bronze, nonvariegated
- ‘Sunglow’ has salmon-orange bicolored flowers and dark green variegated foliage.
- ‘Tango’ can be grown from seed. It has extra-large orange flowers that are set against handsome foliage on 15-inch plants.
Interspecific Impatiens: Interspecific Impatiens (which are hybrids between New Guinea impatiens and other downy mildew resistant Impatiens species) thrive in shade to full sun situations and have downy mildew resistance.
Interspecific Impatiens series include:
- Bounce™ series grows 14 to 20 inches tall and 14 to 20 inches wide in partial sun. They are low maintenance and fast flowering.
- Big Bounce™ series grows 20 to 30 inches tall and 20 to 36 inches wide in partial sun. Similar to the Bounce™ series with larger blooms.
- SunPatiens® Compact Series grows 14 to 32 inches tall and 14 to 24 inches wide in partial shade to full sun. Continuous color persists until frost.
- SunPatiens® Spreading Series grows 18 to 36 inches tall and 24 to 36 inches wide in partial shade to full sun. Ideal for baskets or “quick fill-in” locations.
- SunPatiens® Vigorous Series grows 24 to 42 inches tall and 24 to 30 inches wide in partial shade to full-sun. Strong stems hold up in rain and wind.
Hybridizers and seed houses are continually introducing new species and cultivars of impatiens.
Originally published 03/99