Rosemary is a Mediterranean herb known for its fragrant, needle-like foliage and woody, shrub-like growth habit. In cooler climates, gardeners often worry if their plant, which appears brown or static after the cold season, has survived the winter. As an evergreen perennial, rosemary requires specific temperature ranges to endure colder months. Understanding the conditions for its survival and the signs of life is key to bringing the herb back into the active growing season.
Rosemary’s Climate Requirements and Hardiness Zones
The survival of an outdoor rosemary plant is largely determined by the local climate, specifically the lowest winter temperatures. Rosemary is a tender perennial, meaning it is reliably hardy in USDA Hardiness Zones 7 through 10. In these milder zones, the plant can remain in the ground year-round, growing into a substantial woody shrub.
Most common varieties of rosemary cannot tolerate sustained temperatures below 15 to 20 degrees Fahrenheit. Cold-hardy cultivars, such as ‘Arp’ or ‘Madeline Hill,’ can withstand temperatures as low as -10 degrees Fahrenheit, extending their range into Zone 6 with ample protection. If the plant’s roots and woody base are not insulated from deep, prolonged freezes, the entire structure may succumb to winter kill. The plant’s ability to “come back” is directly proportional to the severity of the cold it endured.
Distinguishing Dormancy from Winter Kill
When a rosemary plant emerges from winter looking dry and brittle, the challenge is determining if it is merely dormant or truly dead. Rosemary is an evergreen, but its growth slows significantly in cold weather, sometimes mimicking a dead plant. The most reliable method to check for life is the “scratch test,” which examines the living tissue beneath the bark.
To perform this test, gently use a fingernail or a small knife to scrape away a tiny section of the outer bark on a stem that appears lifeless. If the tissue immediately beneath the bark, known as the cambium layer, is bright green and moist, the stem is still alive and will likely resume growth. If the scraped area is brown, dry, or brittle, that section of the plant has died and will not recover.
Often, the tips of the branches may have died back due to cold exposure, but the lower stems or the crown near the soil line may still show green, indicating a viable root system. Therefore, test multiple areas toward the base of the plant. Even if all the above-ground wood is brown, new shoots may still emerge from the living roots below the soil surface.
Timing the Spring Revival
Rosemary is characteristically slow to emerge from its winter rest compared to other spring-waking plants. Gardeners should exercise patience, as new growth will not appear until consistent soil and air temperatures signal the end of the frost period. This often means waiting until late spring, typically April or May, depending on the specific region’s last hard frost date.
The plant needs the soil to warm significantly before it begins active growth. The first signs of revival appear as small, soft, light green tips emerging from the stems. These tender shoots are frequently seen low on the plant, near the crown where the stems meet the soil, as this area was the most insulated during winter. Waiting until these clear signs of life appear prevents the accidental pruning of dormant but viable growth.
Ensuring Successful Regrowth
Once the rosemary plant shows definite signs of new growth, post-winter maintenance can maximize its recovery and shape. The first step is to prune away any wood that failed the scratch test, cutting back to just above a node where the green, living tissue begins. Removing this dead wood redirects the plant’s energy toward the healthy, growing sections.
It is important to avoid severe pruning into the old, woody parts of the plant that lack foliage, as new growth does not readily sprout from this old wood. Post-winter care also involves a gradual adjustment to moisture levels. While rosemary requires well-drained soil, its roots need water to fuel spring growth. Increase watering only after the top inch or two of soil has fully dried out.
Established in-ground rosemary plants rarely require fertilizer. However, potted plants that may have depleted their container soil can benefit from a light, half-strength application of a balanced fertilizer as the days lengthen.