Culture
Winter hardy to USDA Zone 8-10 where it may be grown in light, slightly acidic, dry to medium, well-drained soils in full sun. Tolerates light shade, but best performance is in full sun. Established plants have good drought tolerance. Performs poorly in heavy clay soils. Wet, poorly-drained soils in winter are usually fatal. If desired, prune plants after bloom to encourage dense foliage growth. Plants may also be pruned to specific shapes. Best propagated by cuttings. Plants are not winter hardy in the St. Louis area where they are typically grown in containers (clay pots best) which are brought indoors in fall and overwintered in a sunny, humid but cool room with good air circulation (powdery mildew often appears when air circulation is poor). Best indoor location is in a sunny southern window. If at least 6 hours of sun per day cannot be provided indoors, then use of supplemental lighting (grow lights) should be considered. Let soil dry out between water applications (dry on top, but not dry throughout). Avoid overwatering which inevitably leads to root rot. Take containers outside in mid-spring after the last frost date.
Noteworthy Characteristics
Salvia rosmarinus, commonly known as rosemary, is a generally erect, rounded, evergreen shrub with aromatic, needle-like, gray-green leaves and tiny, two-lipped, pale blue to white flowers. It typically grows to 4-6’ tall in areas where it is winter hardy. The intensely fragrant foliage of this shrub is commonly harvested for a variety of purposes including culinary flavorings, toiletries and sachets. These plants also add excellent ornamental value to borders, herb gardens, patio areas and foundations both when grown in the ground and/or as container plants which are often brought indoors for overwintering. Rosemary is native to dry scrub and rocky places in the Mediterranean areas of southern Europe to western Asia. Gray-green, linear, needle-like leaves (to 1.5” long) are closely spaced on the stems and are very aromatic with a strong flavor. Tiny, two-lipped flowers bloom in axillary clusters along the shoots of the prior year’s growth. Where grown outdoors in USDA Zones 8-10, flowers typically bloom from January to April. Some sporadic additional bloom may occur in summer or fall, particularly if plants are trimmed after the late winter to spring bloom. Container plants overwintered indoors will typically bloom later (late spring into summer). Flowers are attractive to butterflies, bees, and other insect pollinators. Synonymous with Rosmarinus officinalis.
The genus name Salvia comes from the Latin word salveo meaning "to save or heal", in reference to the purported medically curative properties attributed to some plants in the genus.
The specific epithet rosmarinus means "dew of the sea", in reference to the native habitat of this species.
‘Arp’ is an upright cultivar that is noted for having excellent winter hardiness (reportedly will survive zone 6 winters with protection). Grows to 3-4’ tall and as wide with light blue flowers. Features small, fragrant, lance-shaped, gray-green foliage (grayer than most other cultivars). Discovered growing in Arp, Texas by Madelene Hill in 1972.
Problems
Rosemary is susceptible to powdery mildew, particularly in humid conditions when air circulation is poor. Botrytis is also a potential concern. Root rots may occur if plants are overwatered. Rosemary is often a difficult plant to overwinter indoors. Watch for aphids, mealybugs, whiteflies and spider mites on indoor plants (less of a problem on outdoor plants). Deer tend to avoid this plant.
Uses
Where winter hardy, grow in herb gardens, rock gardens, seaside gardens, borders or foundations. Ornamental specimen or low hedge. Container plants are attractive additions to patios, decks and other sunny areas around the home.
Leaves may be used (fresh or dried) in a variety of cooking applications such as stews, breads, stuffings, herbal butters or vinegars. Leaves also provide excellent flavor to meats, fish and vegetables. Leaves and flowers are used in sachets. Oil is commercially used in some perfumes, soaps, shampoos, lotions and other toiletries.
Rosemary has a long history of uses for a variety of medicinal and curative applications, some of which are of unsubstantiated value.