Rosmarinus officinalis (Rosemary)
 

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February is a good time to fertilize trees, shrubs and evergreens, says Dr. Susan Hamilton. . .
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UT Gardens' Plant of the Month: Rosemary

Rosemary means "dew of the sea." It’s an appropriate name for this traditional garden herb that is native to the arid coastline of the Mediterranean. There it is watered by ocean mists.

Rosemary (Rosmarinus officinalis) is a tender shrub. Its glossy, strongly scented, evergreen leaves are needle-like with a flashy light stripe underneth. Most rosemary cultivars have an upright form and can grow up to 6 feet tall. Prostrate forms creep along the ground. Depending upon the cultivar, flowers can be either blue, lavender, pink, or white. Various cultivars bloom at different times of the year.

Most selections of rosemary are cold hardy only to zone 8, but five cultivars are known to be hardy to winter temperatures common in Tennessee (zone 6 or 7, depending on your location in the state).

Numerous landscape uses add to rosemary’s popularity. It can be clipped into an impressive herbal hedge or shaped into a fancy topiary. Bonsai forms will work well for those who have enough patience. Rosemary also can be a focal point in a mixed perennial border.

Rosemary is a must in a fragrance garden, and it's the cornerstone of a drought-tolerant garden. The prostrate forms look bountiful in containers and hanging baskets, and they create an impressive evergreen ground cover as well.

Unless you grow a cold-hardy selection, rosemary must spend the winter indoors. Even indoors, good air circulation is required for survival. If you try a cold-hardy selection, I recommend these upright cultivars: ‘Salem’, ‘Hill Hardy’, ‘Arp’, and ‘Athen’s Blue Spires’. ‘Dancing Waters’ is an impressive cold-hardy creeping selection. All of these cultivars are on display in the UT Gardens. (For more information, visit the Gardens at http://utgardens.tennessee.edu.)

Rosemary prefers a well-drained soil with a pH range of 5 to 8. It performs best in full sun but can tolerate partial shade. Most selections do well when planted 2 to 3 feet apart. During the growing season, pinch back growth tips 2 or 3 inches to promote bushy plants. Cut them back hard only in the early spring to allow new growth time to mature. Plants can be pruned lightly throughout the growing season to control shape.

Non-cold-hardy cultivars should be grown in pots where they can be brought indoors during winter. Be sure to place them in a sunny window or under artificial lights. Use well-drained potting mix, and be careful you don't over water them. Soggy soil induces root rot diseases.

Rosemary is not a heavy feeder. For plants grown in the ground year round, fertilize every spring with a well-balanced fertilizer labeled for perennials. For those grown in containers indoors, fertilize them just during the growing season with either a slow-release or water-soluble fertilizer. Be sure to follow label directions.

You can start new rosemary plants by air-layering or from stem cuttings. Rosemary will grow from seed. The process is slow, however, and the seedlings are not true to cultivar. Plants can be set out in the spring when the weather has warmed. (Cold-hardy types can also be set out in the fall.)

Beyond the garden, rosemary has numerous uses. It has a strong flavor and can be used dried or fresh (snip or mince finely) in a bouquet garni with chicken, meat, vegetable, and tomato dishes. Remove the leathery sprigs before serving. As a leaf tea, rosemary can be soothing to an upset stomach.

Dried rosemary is popular in sachets.

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Dr. Susan Hamilton is an associate professor of ornamental horticulture in the University of Tennessee Department of Plant Sciences and director of the UT Gardens. The UT Gardens are located on Neyland Drive in Knoxville. They are open seven days a week during daylight hours.

 
     
 

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