Impatiens

There are two main groups of ornamental impatiens, Impatiens walleriana and New Guinea impatiens. They look quite different but they can be treated the same in general. 

• The walleriana cultivars are the most common but are very susceptible to downy mildew diseases. They were nearly wiped out completely due to a bad disease outbreak but are now making a comeback as tolerant downy mildew resistant cultivars are being developed. Walleriana cultivars typically need to be grown in the shade.
• New Guinea Impatiens are often more sun tolerant and have more resistance to mildew diseases. They also have larger, showier foliage than walleriana cultivars. 
• Both are grown for their brightly colored flowers. Impatiens grow to a height of 6-30 inches depending on the cultivar.

Recommended varieties

Annual impatiens are evaluated as part of the U of M flower trials and research. Located at the WCROC in Morris, MN, the Horticulture Display Garden serves as an All-America Selections (AAS) Display Garden and Trail Grounds and provides the public an opportunity to view superior performers.

The following annual Impatiens cultivars were rated good to excellent in our recent trials:

• Beacon™ series
• Rockapulco® Orange
• Bounce™ Pink Flame
• New Guinea Sunstanding series
• New Guinea Divine™ Orange
• New Guinea Wild Romance Blush Pink

Growing outdoors

Impatiens grow well in both garden beds and in containers or hanging baskets. They can be planted outdoors once soil temperatures are above 60 degrees F. If planting in the garden, plants should be spaced at 8 to 12 inches. Follow these guidelines when choosing a site for impatiens:

• Depending on the cultivar the site might need to be full shade, partial shade or full sun. New Guinea impatiens are much more sun tolerant than Walleriana.
• Soil must be well drained. To improve drainage, compost or sand can be incorporated into heavy soils.
• Impatiens require a lot of moisture so soil must also be able to retain water well in addition to having good drainage. Adding compost or other organic matter can help a sandier soil retain moisture.
• Impatiens prefer soils with a pH of 6-6.5 with a high organic matter content. 

Fertilization and watering

• Incorporate a granular general-purpose fertilizer with equal amounts of nitrogen, phosphorus and potassium into the soil at the time of planting.
• After planting, impatiens should be fertilized monthly using either a granular, water-soluble or a foliar fertilizer that contains higher amounts of phosphorus than nitrogen to promote new flower development over foliage growth.
• When using a granular fertilizer, be sure to incorporate it into the soil by watering or time your fertilizing schedule with natural rain events.

Impatiens are moisture-loving plants that require frequent watering and watering needs will differ depending on the environment the plant is placed into. A plant in full sun will require more water than one in the shade and plants grown in containers will require much more frequent watering than those grown in garden beds. 

• Only water when the top 1-2 inches of soil is dry if growing in a garden bed.
• Water daily for container plants but make sure the container has drainage holes at the bottom to allow excess water to run out. 
• Hanging baskets will require watering at least once a day and should also have drainage holes.
• If the plant starts dropping or losing leaves, that is a sign it is not getting enough moisture.

Pests and diseases

Impatiens do have some pest and disease issues that will need to be taken care of several times throughout the season.

Deer and rabbits enjoy eating the succulent stems so a repellant should be used, either a spray-on or a granular repellent will work. 

Impatiens tend to have issues with downy mildew diseases and, if infected, may need to be treated. Once the plant is infected, there is no cure. If you want to try controlling the spread of the disease, a general-purpose fungicide can be sprayed on the plant to treat the disease and will likely need to be treated several times throughout the season.

With both repellants and fungicides, be sure to follow the product label for proper applications.

Tips for abundant flowering and healthy plants

• With walleriana cultivars, the top 2 inches of the plant can be clipped off right above a leaf node when it is about 6 inches tall. This will result in a bushier plant.
• Be sure to keep the soil surface free of debris and weeds to help prevent a disease outbreak. 
• If only a small number of the plants are showing disease symptoms it may be best to just remove those plants rather than treating all of them.
• If downy mildew becomes a major problem in your garden, you should consider not planting walleriana for a year or two.
• Removing old flowers is not necessary and will not promote new flower growth.

Starting seeds indoors

Walleriana and New Guinea cultivars have slightly different requirements for starting seeds. New Guinea seeds should be started 12 weeks prior to the anticipated outdoor planting date and walleriana seeds need less time and can be started 10 weeks before planting. Use a growing media specifically designed for germinating seeds.

Follow these guidelines for successful seed propagation:

• Plant on media surface and cover with vermiculite.
• Keep the seed and media moist by using a plastic cover over the seeding tray.
• Seeds require light to germinate.
• Walleriana seeds will germinate in 5-15 days at 72-77°F.
• New Guinea seeds will germinate in 12-25 days at 75-80°F.
• After germination, both types can be grown at 65-70°F.