Rosemary, Rosmarinus officinalis
, is an erect, bushy evergreen shrub in the family Lamiaceae grown for its leaves which are used as a herb. The rosemary plant is usually erect in growth habit and possess branched woody stems with tufts of leaves. The leaves are opposite and usually bladelike and glossy green. The plant produces clusters of 5–10 blue, purple or pink flowers on short lateral branches and small oval fruit. Rosemary plants can reach 2 m (6.6 ft) in height and can be productive for many years (up to 30 if conditions are favorable for its growth). Rosemary originates from the Mediterranean.
Rosemary flowers close-up
Rosemary leaves can be used fresh or dried as a herb in cooking or in salads. The leaves and flowers can be used to extract rosemary oil which is used as a seasoning or as a scent in soaps and household products.
Rosemary is suited to both temperate and subtropical areas with most varieties growing optimally at temperatures between 6 and 24°C (39–75°F) in a well-draining loamy soil with a pH between 6.0 and 7.0. Rosemary plants require at least 6 hours of sun every day, direct sunlight being best. Rosemary can survive mild winters but will not tolerate temperatures that are regularly below -3°C (26.6°F). Established rosemary is very drought resistant.
Rosemary can be propagated from seed, cuttings, or by air layering. Seeds germinate slowly, emerging after 3–4 weeks, and have a low germination rate so vegetative propagation is preferred. Cuttings should be taken from healthy, vigorous plants by taking a clipping about 7.6 cm (3 in) in length from the end of a branch. The leaves should be removed from the lower half of the cutting before planting in light textured potting media to root. The cutting should be watered regularly and kept moist, but not wet while they root. The new plants will be ready for transplanting after approximately 8 weeks. after hardening, transplants should be planted 45 cm (18 in) apart allowing 1.2 m (4 ft) between rows.
General care and maintenance
Rosemary is very prone to root rot and should therefore be planted in a well-draining soil and watered sparingly. Allow the soil to dry before watering, generally watering once every 1–2 weeks is sufficient but watering should be adjusted to suit climatic conditions. Plants will benefit from the regular addition of a balanced fertilizer. A layer of mulch will protect the plants over winter.
Rosemary can be harvested as soon as the plant is established in the the ground and has reached a suitable size. Branches are harvested by cutting the terminal growth (25–30 cm/9.8–11.8 in) before they become woody. Rosemary can be harvested several times in one season but it is important to allow the plant to recover and replace growth before the next harvest.
Common Pests and Diseases
Galls of various sizes on roots and root crown below the soil line; galls may occasionally grow on the stems; galls are initially light colored bulges which grow larger and darken; galls may be soft and spongy or hard; if galling is severe and girdles the stem then plants may dry out and die
Only plant disease-free material; plant rosemary in well-draining soils; avoid wounding the plants as much as possible
Leaves yellowing; white-gray fuzzy or downy growth developing on leaves
Promote good air circulation around plants by using adequate spacing; avoid wetting the foliage by watering the plant at the base
Cottony soft rot
Plants rapidly wilting and dying, often without turning yellow; as plants dry out they may turn straw yellow in color; small black fungal bodies (sclerotia) may be present on the surface of the root just below the soil line together with white fluffy mycelium; water soaked lesions may be present on the stem in Spring; infected tissues dry out and may become covered in white mycelium
Plant only disease free material; if disease is known to be present rotate crops with non-hosts such as cereals which are a non-host