According to The United States National Arboretum, the two most commonly grown hardy rosemary cultivars are Rosmarinus officinalis "Arp" and R. officinalis "Madelene Hardy" (syn. "Hill Hardy"). The "Arp" cultivar originated in northern Texas and grows from 3 to 5 feet high. It has pale blue to white flowers. "Hill Hardy" is hardy to zone 6. It grows to 3 feet in height. In general, larger rosemary plants, with the thinnest leaves and the lightest color flowers, are hardier, while prostrate cultivars that hug the ground are the least hardy.
Tall versions of rosemary grow into substantial shrubs with fragrant flowers. R. officinalis "Miss Jessop's Upright" is a popular hardy cultivar that originated in England. It grows from 5 to 8 feet tall and has slate blue flowers. R. officinalis "Tuscan Blue" grows from 4 to 6 feet tall and has dark lavender-blue flowers. It is favored by chefs.
Some varieties of rosemary grow out instead of up, creating a rounder bushy plant. R. officinalis "Benenden Blue" grows to 3 feet and has thin needles and deep blue flowers. This variety has a strong pine fragrance but is not suitable for cooking. R. officinalis "Salem" grows from 1 to 3 feet and has showy, fragrant blue flowers.
Prostrate versions of rosemary grow close to the ground and are less winter-hardy than other varieties. R. officinalis "Logee's Blue" grows from 1 to 2 feet tall and has medium blue flowers. This cultivar is an upright and suitable for bonsai training. R. officinalis "Prostratus" is a creeping variety of rosemary that will grow from 1 to 3 feet high and has pale blue flowers. It is often used for cooking. R. officinalis "Lockwood de Forest" is a semi-prostrate variety that grows up and out, reaching a height of 1 foot. It has glossy dark-green leaves.