Rosemary is botanically classified as a perennial shrub, meaning it is capable of living for many years. Its ability to survive winter depends entirely on the local climate. Gardeners in warmer regions treat the herb as a permanent fixture, while those in colder zones must treat it as a temporary annual or provide protection. The plant, now known as Salvia rosmarinus, is a woody evergreen native to the Mediterranean region.
Rosemary’s True Botanical Nature
Rosemary is an evergreen woody perennial shrub. Its perennial nature is evident in its stems, which become lignified, or woody, providing the structural strength needed to support the plant for decades. This structure allows it to regrow new, softer growth each spring from its established base.
The plant is generally winter-hardy in USDA Plant Hardiness Zones 8 through 11, where temperatures rarely fall below 10°F (-12°C). In these mild climates, rosemary can grow into a substantial, long-lived shrub. In regions falling into Zone 7 and below, the plant functions as a “tender perennial” because its tissues cannot handle sustained freezing temperatures. This cold sensitivity requires gardeners to replace the plant yearly or bring it indoors for winter protection.
Growing Rosemary for Year-Round Harvest
Successful cultivation requires replicating rosemary’s native Mediterranean environment, starting with the soil. The plant demands well-drained, sandy, or rocky soil because it is highly susceptible to root rot in wet conditions. It performs best in a slightly acidic to neutral pH range of 6.0 to 7.0, and often thrives on neglect rather than rich garden beds.
Rosemary is a sun-loving plant that requires a minimum of six to eight hours of direct sunlight each day for optimal growth and flavor. Once established, it is drought-tolerant, meaning watering should be infrequent and only when the soil has dried out completely. Overwatering is the primary cause of decline, especially when grown in containers.
Pruning is necessary to encourage a dense, bushy shape and prevent the plant from becoming woody and sparse. Harvesting sprigs throughout the year serves as light pruning. Gardeners should avoid cutting into the oldest, thickest woody stems, as this can hinder recovery. Never remove more than one-third of the plant’s total growth at any one time, focusing on the soft, new growth at the tips.
Strategies for Cold Weather Survival
In zones colder than its reliable perennial range, gardeners must prepare rosemary for winter.
Outdoor Protection
For plants in borderline zones (Zone 7 and sheltered Zone 6), outdoor protection can be effective. This strategy requires ensuring the plant is in a location with excellent drainage that will not become waterlogged when the ground freezes.
Provide a thick layer of dry mulch, such as straw or shredded leaves, around the base before the first hard freeze to insulate the roots and regulate soil temperature. A windbreak can protect the evergreen foliage from desiccation caused by harsh winter winds. Give the plant a deep watering two weeks before the first expected frost, allowing the stems and leaves to take up moisture to combat winter drying effects.
Indoor Overwintering
For gardeners in truly cold regions, overwintering rosemary indoors as a container plant is the most reliable method. The transition should begin before the first hard frost, ideally by potting up in-ground plants in late summer or early fall for acclimation. Place the potted rosemary in a bright, cool location, with temperatures ideally between 50°F and 60°F, such as a cool sunroom or unheated garage with a window.
During its indoor dormancy, the plant’s growth slows significantly, requiring a drastically reduced watering schedule. The soil must be allowed to dry out almost completely between waterings to prevent root rot, which is particularly dangerous in cool, low-light conditions. Providing bright light, possibly supplementing with a grow light, and ensuring the plant is not placed near heat vents are the best ways to keep the rosemary healthy until it can be moved back outside after the danger of frost has passed.