First introduced into the United States by Longwood Gardens in 1970, New Guinea impatiens comprise hybrid impatiens that possess more rigid and ornate foliage and brightly colored flowers in comparison to the usual impatiens (Impatiens walleriana). Moreover, New Guinea impatiens were bred for their tolerance of sunnier garden locations. Not surviving frost, these plants will be evergreen perennials in U.S. Department of Agriculture winter hardiness zones 9 and warmer.
Starting New Plants
In order to maintain the exact same physical qualities of the mother plant, New Guinea impatiens are propagated by cuttings, not seeds (which yield variable progeny). The 2-inch-long stem cuttings that have no more than two leaves on them are placed in sterile, soil-less potting media in containers. According to Auburn University, the cuttings will take root in about 14 days if the cuttings are misted during the day and kept at a temperature between 70 to 75 degrees F.
Once cuttings have developed their root systems and begin growing new leaves, plants can be transplanted to the garden if there is not threat of frost. Choose a site that has bright indirect light most of the day, but as much as six hours of direct sun rays during the day. Ideally, ensure that the direct sunlight hits the plants either in the early morning or early evening. If the direct sun rays reach the plants in midday, wilting may occur. In cool summer regions (such as in southern Canada, central Europe and the northernmost United States) more sunlight is tolerated, but in long, hot summer regions more bright shade is recommended. Be aware that insufficient light will cause the variegation or special leaf colors on New Guinea impatiens to dull, and flowering may also diminish.
In the garden setting, choose an area that has a moist, well-draining soil (sandy or loam) that is crumbly and rich in organic matter. It is best to avoid soil that is alkaline in pH (over 7.2). Avoid soils that are heavy clay or remain soggy after irrigation or rain. In containers, plant New Guinea impatiens in a soil-less potting mix. Do not use a topsoil as it will compact and harden in the container.
According to the plant breeders at Oglevee Limited, a subsidiary of the Paul Ecke Ranch, New Guinea impatiens need a lot of watering to remain lush and healthy. Apply water to keep the soil evenly moist, but not soggy, which encourages fungal diseases. These hybrid impatiens can slightly wilt without detriment as they will quickly rebound if watered promptly. Hotter temperatures, sandier soils, more direct sunlight, and plants grown in containers are circumstances that warrant more frequent monitoring and watering.
New Guinea impatiens need a fertile soil—often that alone will sustain plants during a summer growing season. Oglevee Limited regards these plants as "moderate feeders," meaning they need some soil nutrition, but do not need a lot of liquid fertilizer applications to perform well. Using a well-balanced water soluble fertilizer (such as 10-10-10) suffices when applied to product label directions and supplied to plants once every two to four weeks. If soils are lacking nutrition, leaves will turn yellow, prematurely drop, or the size of flowers will be smaller than usual. Also, if soils lack magnesium, the foliage will become yellow-green. A tablespoon of epsom salts (magnesium sulfate) in a gallon of water can be applied at any time and repetition to New Guinea impatiens to prevent leaf yellowing.