Impatiens are flowering plants of the Balsaminaceae or balsom family. The genus is large, with more than 850 species, mostly native to parts of Asia and Africa. According to the Missouri Botanical Garden, the most popular variety of impatiens in the United States is Impatiens walleriana, sometimes known as "Busy Lizzy." This ubiquitous bedding plant is not tolerant of temperatures below 32 degrees Fahrenheit and is usually grown as an annual.
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Impatiens walleriana are hardy outdoors in USDA zones 10 and 11, where minimum winter temperatures range from 30 to 40 degrees Fahrenheit. In all other zones, they should not be planted outside until night temperatures are above 50 degrees and soil has warmed up. This is generally in mid-spring when cell packs of young plants become available in garden centers and nurseries. The plants can also be started from seed eight to 10 weeks before the last frost date for a specific area.
Hardiness: Impatiens hawkeri
Another popular impatiens species is Impatiens hawkeri, also known as New Guinea impatiens. These generally have larger flowers than the walleriana species and elongated leaves, sometimes with variegation. These impatiens are also tender in cold winter climates and are hardy outdoors in the same USDA zones as the walleriana impatiens. Unusual specimens can be overwintered indoors and should be brought inside and placed on a sunny widowsill well before the first frost.
Hardiness: Other Impatiens
Impatiens balsamina is sometimes known as "rose balsam" or "garden balsam." It resembles a double-flowered version of the walleriana species and is a true annual. It thrives in the same temperature conditions as Impatiens walleriana and hawkeri but needs somewhat more sunlight. A Chinese species, Impatiens omeiana, also known as "hardy impatiens," is more hardy than the walleriana or hawkeri species and can survive winter temperatures as low as 10 degrees Fahrenheit (USDA zone 6).
Though the most frequently cultivated species of garden impatiens grow well in temperatures between 50 and 90 degrees Fahrenheit, they do require shady locations. The plants are intolerant of drought and should be watered frequently during dry spells. The fleshy stems become elongated or "leggy" as the plants age and should be pinched back to stimulate additional flowering and keep the plant compact. Feed regularly with a balanced fertilizer throughout the growing season, as impatiens, like many annuals, need lots of nourishment.