Rosmarinus — Rosemary
The botanical name Rosmarinus is derived from old Latin for 'dew of the sea', possibly for its origins in coastal Mediterranean areas. Rosemary was valued by the ancients as a sacred and medicinal plant and continues to have numerous herbal and culinary uses among many cultural groups. Of the dozens of forms ranging from groundcovers to tall shrubs, all belong to only one species, Rosmarinus officinalis, all edible but with somewhat differing flavors.
Sited in full sun or part shade, rosemary never falters in hot summers or cold, wet winters once it become established after a year or so in the ground. Newly planted, it requires ample water to keep the root ball moist. It adapts to any soil with no need for fertilizers. In the hottest months, occasional irrigation may be needed for young plants; otherwise, rosemary is drought tolerant.
Long bloom is among its finest attributes. Small tubular blue flowers that range from almost sky blue on ‘Blue Spires’ to the deepest azure on ‘Santa Barbara’ attract bees and hummingbirds from mid-autumn until spring when butterflies begin to feed. A few cultivars bloom in pink or white. Other animals, including deer do not touch its sappy, fine, dark-green needle foliage that is pungently fragrant when crushed.
Rosemary is an evergreen perennial classified as a subshrub for the woody lower stems that develop over time. It can be let go like a wild plant to reach in all directions with its twisting branches, or pruned to stay more compact. Generally, it should not be pruned hard back into thick bare wood, only into thinner branches bearing foliage.
Forms are essentially stiffly upright, mounding, or prostrate in habit. Upright forms grow 4-5 ft. high by 5-6 ft. across. There are a number of dwarf forms with vertical branching for sites where more compact form is desired. Long, straight branches are favored for use as wands on barbeque grills. Popular selections include 'Blue Spires' (to 3-4 ft.) and 'Tuscan Blue' (to 5-6 ft.).
Mounding rosemarys are most common and the most versatile. They may be planted as specimens, among perennial beds, trained as topiaries, sheared as hedges, or used as bank covers or free-form groundcovers.
‘Collingwood Ingram’ and similar ‘Ken Taylor’ are popular mounding cultivars for their bright blue, nearly violet flowers and curved branches, but neither lends typical flavor for culinary use. Preferred flavors are found in ‘Majorca Pink,’ ‘Huntington Carpet,’ ‘Irene,’ and in semi-upright ‘Arp’ and ‘Hill Hardy’ among others. Seedlings of any named variety may revert to the original species form, unpredictable in shape and flavor, although most species plants are suited for culinary use. Personal taste, however, is the final arbiter.
Gardeners seeking reliably low, prostrate forms are well advised to purchase only those plants with labels specifying height. Prostrate forms stay low and spreading, perfect for planting on a rock wall or terrace where the foliage cascades down the face, looking like the hanging gardens of Babylon. They also constitute an almost-walk-on groundcover.
Propagate rosemary from cuttings of non-flowering branches in early summer, or layer established low branches by scooping a shallow trench, burying the branch, and putting a rock over it to keep it from springing up. This procedure is best done during the rainy season. There should be enough roots on the new plant in a few months to detach and transplant it.
Rosemary may be grown indoors in a sunny window as a culinary herb. Stems may elongate rapidly and require frequent snipping for grinding or use as an herbal decoration for dishes. Indoors, plants may be short-lived. With a bush or two outside the kitchen door, it’s easy to step out and snip a few sprigs.