Rosemary (Salvia rosmarinus) is a fragrant, flavorful herb beloved in many gardens and kitchens. Its distinctive piney scent and woody stems make it instantly recognizable, but its life cycle often causes confusion for gardeners. The question of whether rosemary is a perennial or an annual plant depends entirely on where the plant is being grown.
Defining Perennial and Annual Plants
The classification of plants as perennial or annual describes the duration of their life cycle. An annual plant completes its entire life cycle—from germination to seed production and eventual death—within a single growing season and must be replanted every year. A perennial plant, by contrast, lives for more than two years, returning season after season from the same root system. These plants survive periods of dormancy, such as winter or drought, and resume growth when favorable conditions return.
Rosemary’s Native Classification and Hardiness
Rosemary is definitively a woody perennial shrub in its native habitat, the warm, dry climate of the Mediterranean. Left undisturbed in ideal conditions, it can grow into a substantial shrub that lives for many years. The plant’s survival is determined by its cold tolerance, which is mapped using the USDA Hardiness Zone system. Most common rosemary varieties are reliably hardy only in Zones 8 through 10, where winter temperatures rarely drop below 10°F (-12°C). Below this range, the plant is susceptible to freezing and death.
Adapting Rosemary Care Based on Climate
In USDA Zones 8 and higher, rosemary should be treated as a permanent fixture in the landscape. Planting it in a location that receives full sun and has excellent drainage is paramount for long-term health. During the winter, little intervention is required beyond ensuring the soil does not remain waterlogged, which can lead to root rot. Mulching around the base of the plant before the coldest period can help insulate the roots.
Gardeners in Zone 7 and colder must approach rosemary cultivation differently, treating the perennial as a seasonal annual plant. The most effective strategy is to plant it in a container, which allows for easy relocation when frost threatens. The plant must be brought indoors before the first hard frost, typically when nighttime temperatures consistently fall near freezing.
Indoor Overwintering
For successful indoor overwintering, rosemary needs a bright, cool environment, ideally with temperatures between 40°F and 55°F (4 to 12°C). A cool sunroom, a bright, unheated garage, or a stairwell provides better conditions than a warm living area. Warm indoor air is often too dry and can encourage pests like spider mites. Watering must be drastically reduced during this period, allowing the soil to dry out between applications to prevent root disease.