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Most varieties of this attractive woody herb are cold-hardy only to Zone 7 or 8, but the 'Arp' cultivar will overwinter in Zone 6 and sometimes in Zone 5 if you can keep the plant in a warm, sheltered location.
'Arp' was released by the U.S. National Arboretum after herb expert Madalene Hill discovered an 8-foot-wide, 40-year-old rosemary growing in Arp, Texas. Tests confirmed the plant to be hardy to –10° to –15°F. While 'Arp' is cold-hardy, Hill recommends growing the young plants in pots that you bring indoors for the first two winters. Keep the potted plants in a sunny window of the coolest room you have. Water lightly, but keep the humidity high by setting the pots on a tray of pebbles and water. Mist the plants daily.
You can plant 2- or 3-year-old plants in the garden, but be sure the site has protection from prevailing winter winds as well as good drainage. Hill warns that rosemary is more likely to die from wind damaging its evergreen leaves than from cold killing its roots.
