Which Type of Rosemary Is Right for You?
Rosmarinus officinalis should be a simple plant to explain. It’s easy enough to describe: an evergreen shrub native to the Mediterranean with dark green, needlelike leaves that have a resinous aroma. From late winter through spring, the plant displays blue flowers. There are two basic types: upright forms useful as shrubs, and prostrate types that will spill down slopes and cascade over walls. So far, so good.
Care is also straightforward. Once rosemary is established, occasional deep watering is almost all it needs. Prune lightly to shape, if desired. Feed little, if at all. The plants will endure drought, heat, wind, and salt spray. Insects leave them alone (the aromatic oils in the foliage act as a natural repellent). And deer and rabbits don’t like the taste.
Rosemary has only two weaknesses. It is somewhat tender―most varieties suffer damage when temperatures dip below the teens. And it is susceptible to root rot―usually a consequence of poor drainage, often exacerbated by overwatering.
Now comes the tricky part: distinguishing between the many varieties on the market. They don’t look much different in nursery containers, and catalog descriptions sound similar too. The fact that one variety may be sold under several names (for example, ‘Collingwood Ingram’, ‘Ingramii’, and ‘Benenden Blue’ are all the same plant) adds to the confusion.
To sort out the differences, we spoke with expert growers. They recommended the varieties listed below.
UPRIGHT SHRUBS (FROM TALLEST TO SHORTEST)
‘Tuscan Blue’, 6 to 7 feet tall. Leaves are wider than average and very aromatic; dark blue flowers. Good shrub for many situations. “The workhorse of the industry,” says David Fross of Native Sons Nursery (wholesale only), in Arroyo Grande, California.
‘Blue Spires’, 5 to 6 feet tall and 4 to 6 feet wide. Strong vertical habit; clear blue flowers. “It looks like a miniature Italian cypress,” says landscape designer Christine Mulligan of Long Beach, California. “If you want a formal look, it’s the best choice.”
‘Miss Jessup’s Upright’, 4 to 6 feet tall and about half as wide. Slender branches; pale blue flowers. Good choice for formal herb garden or confined spaces.
‘Gorizia’, 4 to 5 feet tall and nearly as wide. Stiffly upright and rather open form. Leaves are larger, longer, and brighter green than typical; pale blue flowers. Good specimen or accent plant. “Very architectural-looking,” says Jeff Rosendale of Sierra Azul Nursery & Garden, in Watsonville, California.
‘Golden Rain’ (‘Joyce DeBaggio’), 2 to 3 feet tall and as wide. Yellow gold leaves; dark blue flowers. Use for contrast against darker green foliage.
‘Boule’, 3 feet tall and wide. A new introduction from Native Sons, it forms a neat dome (boule means “ball” in French).
‘Collingwood Ingram’ (‘Ingramii’ or ‘Benenden Blue’), 2 to 2 1/2 feet tall and 4 feet wide or wider. “Because it’s always putting out new side growth, you never see woody trunk,” says Mulligan. This habit makes it well suited for slopes (the garden shown on page 78 is a good example). This rosemary also mixes nicely with ceanothus, rockrose, and other drought-tolerant shrubs.
‘Ken Taylor’. Similar to ‘Collingwood Ingram’ but slightly shorter and somewhat trailing. Showy dark blue flowers. Best on slopes. Sensitive to root rot.
Linda Lamb Peters
‘Prostratus’, 2 feet tall and 4 to 8 feet wide. Pale blue flowers. Most commonly used rosemary for cascading down walls, as in the photo at left of the garden designed by Carole McElwee of Capistrano Beach, California. Fairly frost tender.
‘Irene’, 1 1/2 feet tall; spreads 2 to 3 feet per year. More hummocky form than ‘Prostratus’ or ‘Huntington Carpet’ (see below). Showy violet blue flowers. Good choice for draping slopes or walls. Hardier (to 15°) than most trailing types.
‘Huntington Carpet’ (‘Huntington Blue’). About half as tall and wide as ‘Prostratus’ (above). Leaf nodes are closer, so the ground cover has a denser appearance. Pale blue flowers. Excellent choice for covering slopes or trailing down walls.
BEST KINDS FOR COLD OR WET CLIMATES
‘Arp’, 4 feet tall and wide. Rather open habit but can be kept denser with frequent pruning. Gray green leaves; bright blue flowers. Hardy to -10°.
‘Hill Hardy’ (‘Madalene Hill’), 3 to 5 feet tall and as wide. Foliage denser and brighter green than ‘Arp’. Hardy to at least 0°.
‘Salem’, 2 feet tall and wide. Fairly tolerant of wet soil, it’s a popular choice in moist areas of the Pacific Northwest.
BEST CULINARY KINDS
You can use any R. officinalis for cooking, but upright kinds with broader leaves contain more aromatic oil. ‘Tuscan Blue’ is the favorite of many chefs, but ‘Blue Spires’ and ‘Miss Jessup’s Upright’ are also good. So is ‘Spice Island’, which is normally sold in the herb section; it grows into an upright, 4- to 5-foot-tall shrub.
Garden centers and nurseries may carry only a few kinds of rosemary, but most can usually order other varieties from wholesale growers on request. Or order plants from the following mail-order suppliers.
Forestfarm: www.forestfarm.com or (541) 846-7269. Sells ‘Arp’, ‘Blue Spires’, ‘Golden Rain’, ‘Spice Island’, and ‘Tuscan Blue’.
Goodwin Creek Gardens: www.goodwincreekgardens.com (800) 846-7359. Sells ‘Arp’, ‘Blue Spires’, ‘Collingwood Ingram’, ‘Golden Rain’, ‘Gorizia’, ‘Hill Hardy’, ‘Miss Jessup’s Upright’, ‘Prostratus’, and ‘Tuscan Blue’.
Territorial Seed Company: www.territorialseed.com or (541) 942-9547. Sells ‘Arp’ and ‘Salem’.
Joseph Masabni and Stephen King Assistant Professor and Extension Horticulturist, and former Associate Professor, Texas A&M Department of Horticultural Sciences; The Texas A&M University System
Rosemary (Rosmarinus officinalis) is relatively easy to grow, making it a good choice for any home herb garden. Its pungent flavor and pinelike scent make rosemary a popular ingredient in foods. The upright varieties are best for both fresh and dried use.
Rosemary can be grown as an annual (completes its life cycle in 1 year) or a perennial (completes its life cycle in 3 or more years). In herb gardens, it is often planted along with thyme, oregano, sage, and lavender. When planting, choose a variety that is suitable to the climate, soil, and desired use.
These varieties are best for Texas:
- Blue Boy
- Dancing Waters
- Golden Rai
- Pine Scented
- Spice Islands
- White Pine
Scented rosemary is best for cooking because of its excellent flavor and soft leaves. Blue Boy, Spice Islands, and White rosemary are also used in cooking. Arp, Dancing Waters, Golden Rain, Pink, and White varieties are more often used as landscape plants.
Rosemary can be grown in pots or in an herb garden (Fig. 1). Most varieties grow best in well-drained, loamy, slightly acidic soil. The preferred soil pH is between 6.0 and 7.0.
Rosemary should receive at least 6 hours of sun each day; it grows best in full sun. If you plan to use rosemary as a perennial plant, choose a site that will not be disturbed by tilling.
Figure 1. Rosemary can be raised in a pot or in a garden.
Follow these steps to prepare the soil:
- Remove all rocks, shrubs, weeds plant debris, and tree roots from the area to be planted.
- Collect a soil sample and have it analyzed to determine your soil’s fertility level. For information about the Texas A&M Soil, Water and Forage Testing Laboratory, visit http://soiltesting. tamu.edu/. 3. If needed, fertilize according to the soil test results to supplement the nutrition added from compost or organic matter. If the pH is too low, add lime to make the soil more alkaline.
- Add about 4 inches of organic matter or compost to the surface and incorporate it with a pitch fork or a rototiller to a depth of 6 to 8 inches. Raised or slightly mounded beds provide the best drainage for the herb.
Like most herbs, rosemary is fairly drought resistant and, if healthy enough, can tolerate a light freeze. It is most successful when grown from cuttings or transplants. Although seed is readily available and usually inexpensive, its germination rate is usually only about 15 percent.
The best way to propagate rosemary is by taking a cutting from an already vigorous plant:
- Clip a 3-inch branch from the stem of the plant.
- Trim off most of the lower leaves to 1½ inches up the stem.
- Plant one or two cuttings into a 3-inch pot.
- Water the cuttings.
- Place the pot in a windowsill with indirect sunlight and temperatures between 60° and 70°F.
- After about 8 weeks, the cuttings will be rooted and ready for transplanting to their permanent location.
Rosemary seldom needs fertilizer. But if growth is slow or the plant appears stunted or pale yellow, apply fertilizer once in early spring before new growth appears. Any allpurpose fertilizer in dry or liquid form is suitable as long as it is applied correctly. To prevent leaf burning, avoid applying fertilizer directly onto the plant.
Too much water can cause root rot. Sometimes it can be difficult to determine when a rosemary plant needs water because its needles do not wilt as broad leaves do. On average, water rosemary every 1 to 2 weeks, depending on the plant size and climate conditions. Allow the plants to dry out thoroughly between each watering.
Although rosemary resists most diseases, some cases of powdery mildew have been reported. To prevent the disease from spreading, check the plants regularly and apply the proper fungicides when needed.
You can reduce the incidence of diseases by pruning overgrown plants to improve air circulation within the plants. Pruning also stimulates them to produce new shoots.
Rosemary is fairly resistant to pests. If spider mites, mealy bugs, or scales do appear, any organic or inorganic insecticide may be used.
If the plant has scales, an easy solution is to clip off and discard the infested plant tips; scales are sedentary insects. For mealy bugs, spray the plants with water, pyrethrum soap, or a soap-based insecticide.
Insects that suck plant sap are generally more prevalent in areas where too much nitrogen fertilizer has been applied. You can avoid most insect problems by fertilizing properly.
Once the plant grows to a suitable size, you can pick several small branches without harming it. Nursery plants can be harvested sooner than cuttings or seeds (Table 1).
TABLE 1. Usual span from planting to harvesting rosemary.
Rosemary plants can be harvested several times in a season, but they should be allowed to replace their growth between harvests. Some varieties are valued for their small flowers, which are harvested for use in salads.
The clippings can be used fresh or dried for later use (Fig. 2). Fresh cuttings will retain their best flavor for 2 to 7 days in the refrigerator. To store rosemary for longer periods, hang it in bundles to dry.
Figure 2. Fresh-cut rosemary will retain its best flavor for 2 to 7 days in the refrigerator.
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