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Rosmarinus officinalis ‘Blue Spires’


Evergreen, Herbs, Shrubs, Flowers


Fine-leafed, aromatic, and evergreen, this Mediterranean shrub fits well in Western gardens. Its genus name means “dew of the sea,” reflecting the plant’s native habitat on seaside cliffs. It does as well with close ocean exposure, but thrives inland too, even with hot sun and poor alkaline soil, if given moderate water and infrequent light feeding. Habit can be stiff and erect, rounded, or prostrate and creeping. Height ranges from 1 to 8 ft.

Plants are thickly clothed in narrow, resinous, aromatic leaves that are usually glossy dark green above, grayish white beneath. Small clusters of 1/4–1/2-in. blossoms in various shades of blue (rarely pink or white) appear through winter and spring; bloom occasionally repeats in fall. Rosemary flowers are edible—add them to salads or use as a garnish—and make excellent honey. Leaves are widely used as a fresh or dry seasoning; thrown onto hot barbecue coals, they produce a heavenly fragrance.

Good drainage is essential. Too much fertilizer and water result in rank growth, subsequent woodiness. Control growth by frequent tip pinching when plants are small. Prune older plants frequently but lightly; cut to side branch or shear. If plants become woody and bare in center, cut back selected branches by half so that the plant will fill in with new growth (be sure to cut into leafy wood; plants will not regrow from bare wood). Branches root wherever they touch the ground; creeping varieties will spread indefinitely, forming extensive colonies. To get new plants, root tip cuttings or dig and replant layered branches.

Cold-hardiness depends upon selection. In general, upright varieties are hardier; prostrate ones (originally from Majorca and Corsica) are more tender, suffering damage at 20°F (–7°C) or even higher. In cold-winter areas, choose the hardiest types and shelter them from winter winds; wrap upright growers in plastic sheeting (leaving top uncovered) in late fall to prevent branches from breaking under weight of snow. Even the hardiest types can succumb to cold if they have wet feet. Beyond hardiness range, grow rosemary in pots and winter indoors on a sunny windowsill.

Use taller types as clipped or informal hedges or in dry borders with native and gray-leafed plants. Lower kinds are good ground or bank covers, useful in erosion control. Set container-grown plants or rooted cuttings 2 ft. apart for moderately quick cover. Foliage of most types has culinary uses, but flavor and fragrance vary; the best have a mildly pungent flavor and a complex aroma with sweet as well as resinous notes. Rosemary is also used in medicines, cosmetics, potpourri, and moth repellents.

Rosemary plants sold without a name are frequently seedlings, which lack the uniformity of cutting-grown, named selections. Unfortunately, variety names are often confused, and many have synonyms; but named plants are still a better bet than nameless plants.

‘Blue Spires’

Strong vertical grower, to 5–6 ft. tall and as wide or wider with age; can be pruned for narrower form. Deep blue flowers. Superb landscape variety; makes a tight-sheared hedge. Excellent for seasoning.

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