Alocasia, known colloquially as elephant's ear, is grown as a houseplant in many parts of the United States. They are non-native tropical plants that will thrive outdoors only in the warmest parts of the country. Zone 7 is at the upper extreme of where they will survive outdoors, and that is only for certain species.
Hardiness Zone Geography
According to Eileen Powell's "The Gardener's A-Z Guide to Growing Flowers from Seed to Bloom," Zone 7 includes parts of Massachusetts, New York, New Jersey, Delaware, Maryland, Virginia, North Carolina, South Carolina, Georgia, Alabama, Mississippi, Tennessee, Virginia, Ohio, Oklahoma, Texas, New Mexico, Arizona, Utah, Nevada, California, Oregon and Washington state.
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Note that hardiness zones are based on climates and maps may change over time. Consult a USDA hardiness zone map, found in the back of many gardening books and on the Internet, to find out if your particular location is included in zone 7.
Varieties That Thrive in Zone 7
According to "The Southern Living Gardening Book," elephant's ears are frost-tender, which means they will die back when cold reaches your area. If the plant is left in the ground over a very cold winter, they may not survive to come up the next spring. The book states that certain types--alocasia cucullata, alocasia macrorrhiza, alocasia odora, alocasia plumbea, alocasia portodora and alocasia wentii--are types that are hardy in zone 7. Other types are only hardy in zones 8 and further south.
Planting Considerations
Elephant's ear should be planted in the spring after the last frost if they are to be grown as outdoor plants. As they are non-native and evolved in a tropical environment, severe cold may irrevocably damage the plant so you must avoid planting them prematurely. In zone 7, the last frost may be as late as May depending on region. Frost dates vary even within the zone, so consult a farmer's almanac or frost date map for guidance about your location.
Generally, when the ground has warmed in the spring to a temperature consistently above freezing, the elephant's ear bulbs or seeds can be planted outdoors. Give the outdoor plants a head-start by starting seeds or bulbs indoors six weeks before the date you will expect the ground to warm, and transplanting them when temperatures are consistently above freezing.
Elephant ear plants that will be grown as houseplants can be cultivated any time of year and in any part of the country. Plant them in well-drained medium such as peat or sand and keep them in a room where they will have temperatures at least 70 degrees Fahrenheit according to Peter Boyce for the International Aroid Society, Inc.