Native to the western Mediterranean, rosemary is one of the few winter-blooming herbs. Under good growing conditions outdoors, this evergreen garden shrub can reach about four to six feet in height with a four foot spread. When grown as a container plant, this tends to be one to four feet tall with about an equal spread. The species has an upright growth habit. However, there are a number of low growing and spreading cultivars available.
A member of the mint family, this features needle-like foliage. The long, narrow, leathery, sharp-pointed leaves are gray-green. With grayish undersides, their edges curve downwards.
Rosemary begins blooming during the winter on old wood from the leaf axils. It continues flowering through the spring. The two-lipped flowers, which resemble those of the other members of the mint family, are usually pale blue. However, cultivars with dark blue, lilac, pink, and white flowers are also available.
Rosemary requires a quick draining soil. If necessary, grow it in a raised bed. This plant prefers a pH between 5 and 8. It does well in poor soils. Full sun is a requirement in most areas. For very hot climates, some partial shade is helpful. This plant will not need watering very often for it is drought resistant. It prefers to be kept dry. Avoid overwatering as this can lead to disease. A general all purpose fertilizer can be used, especially if you plan to harvest stems on a regular basis.
Considered winter hardy to zones seven, this plant can be damaged by very low temperatures. It is sometimes possible to grow the hardiest ones, such as Arp, outdoors in zone six. In some cases, this particular cultivar has even survived in zone five if it is given a very sheltered position. This plant originated in Texas, and can tolerate temperatures from -10 to -15 degrees Fahrenheit. Typically, here in western North Carolina in zone 6, some kinds of rosemary survive for a number of years only to be killed when there is a particularly cold winter.
In cold climates, rosemary growing in containers can be overwintered indoors. It needs a relatively cool, sunny place with temperatures going as low as 35 to 45 degrees Fahrenheit during the night. What this means is that hot greenhouses and conservatories really aren't very suitable. Rosemary doesn't respond well to dry, overheated rooms. When I lived in zone 5, I kept it in a sunny, unheated room, and it did just fine.
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