Rosemary is a herb with pale flowers and evergreen leaves. It gives off a distinctive scent and is used in cooking as well as in the making of scented perfumes, soaps, and candles. Rosemary is native to the Mediterranean region where evidence of its use by humans dates back at least 7000 years.
I. Appearance and Characteristics
Salvia rosmarinus, commonly known as rosemary, is a shrub with fragrant, evergreen, needle-like leaves and white, pink, purple, or blue flowers, native to the Mediterranean region. Until 2017, it was known by the scientific name Rosmarinus officinalis (), now a synonym.
It is a member of the sage family Lamiaceae, which includes many other medicinal and culinary herbs. The name rosemary derives from Latin ros marinus (lit. ’dew of the sea’). Rosemary has a fibrous root system.
Rosemary is an aromatic evergreen shrub with leaves similar to hemlock needles. It is native to the Mediterranean region, but is reasonably hardy in cool climates. Special cultivars like ‘Arp’ can withstand winter temperatures down to about −20 °C (−4 °F). It can withstand droughts, surviving a severe lack of water for lengthy periods. It is considered a potentially invasive species and its seeds are often difficult to start, with a low germination rate and relatively slow growth, but the plant can live as long as 35 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 (1⁄16–3⁄16 in) 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).
II. How to Grow and Care
Sunlight
Salvia rosmarinus requires full sun, which is generally defined as a minimum of six hours of direct sunlight daily. There are varieties that will also tolerate partial shade. They are facultative long day plants and flower induction occurs more rapidly under long days. They will flower under any photoperiod, but will flower quicker and better under long days.
Until plants become established, some protection from extreme winds and direct, hot sunlight may be necessary. Good air movement is also important.
Temperature
Rosemary can grow in USDA zone 8-10. It grows best at the temperature of 16 – 19 °C. Once plants reach a saleable size, they can be moved to an open environment with good air movement. Plan ahead on this step because the plant grow very fast coming out of dormancy and can get leggy very quickly if grown too warm.
Watering
Rosemary are very drought tolerant and will do better in drier soil than overly moist soil. Lightly water when the top 2 inches of soil is dry. Keep the soil evenly moist during all stages of growing. The plants requires average amounts of irrigation, and overly wet conditions will promote tall, leggy growth.
Soil
Fertilizing
Salvia rosmarinus are light feeders and only occasionally need fertilizer. A light application of a balanced fertilizer or compost in early spring, after new growth appears, can be sufficient. Keep granular fertilizers away from the plant crown and foliage to avoid burn injury. Use low rates of a slow release, as higher rates may encourage root rots.
Planting Instructions
Pruning
Trimming and pinching can be done early when a fall planting is done. Pinching 2 to 4 weeks after transplant in the fall can assist in building a plant that has a thicker form and also give you more flowers spikes per pot. Trimming is not recommended when forcing plants in the spring or on plants that have been freshly planted in the spring from cooled liners.
Remove spent flower spikes to encourage flowering and prevent seed development. Pinching the growing tips of plants can encourage bushiness.
Mulching
Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating.
Mulches help retain soil moisture and maintain even soil temperatures. For annuals an organic mulch of shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.
Propagation
If you would like to propagate your own rosemary plant, the best option is to start with a cutting. Not only is this an inexpensive way to get a new plant but taking cuttings from a mature plant can help to promote more branching and bushier growth. The best time to take a cutting is in the spring or summer. Here’s how:
- Cut a piece of healthy stem that’s a few inches long. Choose new softwood growth for best results.
- Remove the leaves on the lower portion of the stem, leaving at least five leaves.
- Dip the cut end in the rooting hormone.
- Plant the cutting in a moist soilless potting mix in a small container that has drainage holes.
- Place the container in a warm spot that has bright, indirect light. Mist the cutting daily, and make sure the growing medium doesn’t dry out.
- In about two to three weeks, gently tug on the stem to check for roots. If you feel resistance, you’ll know roots have developed. After that, the cutting is ready for transplanting.
How to Grow from Seed
Growing rosemary from seeds can be difficult because they don’t germinate easily and they often do not grow true to their parent plant. If you wish to try growing rosemary from seed, plant several more seeds than the number of plants you hope to grow. Start seeds around three months prior to your area’s projected last frost date in the spring. Take these steps:
- Soak the rosemary seeds for 24 hours before planting, which improves germination.
- Scatter the seeds in a tray filled with moist seed-starting mix, just lightly covering them with the mix.
- Cover the tray with plastic wrap to trap moisture, and make sure the mix doesn’t dry out.
- Place the tray on a heat mat to keep the soil between 80 degrees and 90 degrees Fahrenheit.
- As soon as seedlings appear, remove the plastic wrap, and place the tray in bright light.
- Once seedlings are around 3 inches high, move them to individual pots or outdoors if the weather is warm.
Potting and Repotting
The soil for rosemary needs excellent drainage so use a potting mix that contains perlite, which helps to keep the soil light, well-aerated, and well-draining. Plan to repot every year into one container size up, using fresh potting mix. The best time to repot is in the spring. Gently loosen the plant from its previous container and situate it at the same depth in the new one, filling around it with soil.
Overwintering
Bring rosemary indoors well before any frost is predicted in the fall forecast. Keep it in a warm room and away from any drafts or drying air from heat vents. Continue providing it with at least six hours of sunlight per day via a bright window and/or grow light. And slightly back off on watering, though don’t allow the soil to fully dry out. Once frost is out of the forecast in the spring, the plant can go back outside.
Pests and Diseases
High humidity and poor air circulation can result in powdery mildew—a white, powdery fungus—on rosemary plants. Powdery mildew typically won’t kill a plant, but the disease will weaken it. To prevent powdery mildew, make sure the plant’s soil isn’t too wet, and provide a few feet of space around it for airflow.
Also, be on the lookout for aphids and spider mites, especially on indoor plants. Use an insecticidal soap as soon as you spot an infestation to prevent it from spreading.
III. Uses and Benefits
Aside from its usage in the fragrance industry, Rosemary is not only used as a decorative plant in gardens, but also cultivated for practical applications, such as medicine and cooking. When the plant is fully grown, the leaves, twigs, and flowering apices are often extracted for use in these areas. The leaves are used to flavor various foods, such as stuffing and roasted meats.
- Cultivation
Since it is attractive and drought-tolerant, rosemary is used as an ornamental plant in gardens and for xeriscape landscaping, especially in regions of Mediterranean climate. It is considered easy to grow and pest-resistant. Rosemary can grow quite large and retain attractiveness for many years, can be pruned into formal shapes and low hedges, and has been used for topiary. It is easily grown in pots. The groundcover cultivars spread widely, with a dense and durable texture.
- Culinary use
Rosemary leaves are used as a flavoring in foods, such as stuffing and roasted lamb, pork, chicken, and turkey. Fresh or dried leaves are used in traditional Mediterranean cuisine. They have a bitter, astringent taste and a characteristic aroma which complements many cooked foods. Herbal tea can be made from the leaves. When roasted with meats or vegetables, the leaves impart a mustard-like aroma with an additional fragrance of charred wood that goes well with barbecued foods.
In amounts typically used to flavor foods, such as one teaspoon (1 gram), rosemary provides no nutritional value. Rosemary extract has been shown to improve the shelf life and heat stability of omega 3-rich oils which are prone to rancidity. Rosemary is also an effective antimicrobial herb.
- Fragrance
Rosemary oil is used for purposes of fragrant bodily perfumes or to emit an aroma into a room. It is also burnt as incense, and used in shampoos and cleaning products.
- Phytochemicals
Rosemary contains a number of phytochemicals, including rosmarinic acid, camphor, caffeic acid, ursolic acid, betulinic acid, carnosic acid, and carnosol. Rosemary essential oil contains 10–20% camphor.
Rosemary extract, specifically the type mainly consisting of carnosic acid and carnosol, is approved as a food antioxidant preservative in several countries. The E number is E392.
- Folklore and customs
The plant or its oil have been used in folk medicine in the belief it may have medicinal effects. Rosemary was considered sacred to ancient Egyptians, Romans, and Greeks. In Don Quixote (Part One, Chapter XVII), the fictional hero uses rosemary in his recipe for balm of fierabras.
The plant has been used as a symbol for remembrance during war commemorations and funerals in Europe and Australia. Mourners would throw it into graves as a symbol of remembrance for the dead. In Australia, sprigs of rosemary are worn on ANZAC Day and sometimes Remembrance Day to signify remembrance; the herb grows wild on the Gallipoli Peninsula, where many Australians died during World War I.
Several Shakespeare plays refer to the use of rosemary in burial or memorial rites. In Shakespeare’s Hamlet, Ophelia says, “There’s rosemary, that’s for remembrance. Pray you, love, remember.” It likewise appears in Shakespeare’s Winter’s Tale in Act 4 Scene 4, where Perdita talks about “Rosemary and Rue”. In Act 4 Scene 5 of Romeo and Juliet, Friar Lawrence admonishes the Capulet household to “stick your rosemary on this fair corse, and as the custom is, and in her best array, bear her to church.” It is also said that “In the language of flowers it means ‘fidelity in love.’”
In the Spanish fairy tale The Sprig of Rosemary, the heroine touches the hero with the titular sprig of rosemary in order to restore his magically lost memory.
Rosemary is very important in Danube Swabian culture being used for christenings, weddings, burials and festivals, for example, an apple with a sprig of rosemary in it is present at Kirchweih celebrations.
IV. Harvesting and Storage
Rosemary can be harvested at almost any time of year, though spring and summer are when it grows most actively. And the leaves are most flavorful and aromatic just before the plant blooms. To harvest, use pruners to cut off 4- to 6-inch stem tips.
Use fresh rosemary sprigs or leaves in cooking as you like. Or hang the stems upside-down in a dry, cool, well-ventilated area for drying, which should take a couple of weeks. Once the stems are dry, strip off the leaves and keep them in an airtight container in a pantry.
