Rosemary is an aromatic evergreen shrub with leaves similar to hemlock needles. It is native to the Mediterranean and Asia, but is reasonably hardy in cool climates. Special cultivars like ‘Arp’ can withstand winter temperatures down to about −20 °C. It can withstand droughts, surviving a severe lack of water for lengthy periods. In some parts of the world, it is considered a potentially invasive species. The seeds are often difficult to start, with a low germination rate and relatively slow growth, but the plant can live as long as 30 years.
Forms range from upright to trailing; the upright forms can reach 1.5 m (4 ft 11 in) tall, rarely 2 m (6 ft 7 in). The leaves are evergreen, 2–4 cm (3⁄4–1+1⁄2 in) long and 2–5 mm broad, green above, and white below, with dense, short, woolly hair.
The plant flowers in spring and summer in temperate climates, but the plants can be in constant bloom in warm climates; flowers are white, pink, purple or deep blue. Rosemary also has a tendency to flower outside its normal flowering season; it has been known to flower as late as early December, and as early as mid-February (in the northern hemisphere).