How to Overwinter Rosemary: Essential Tips

September 29, 2024 3 min read

Rosemary is hardy enough to withstand temperatures as low as -7°C (20°F).

While Rosemary is frost-hardy, it is crucial to protect it from prolonged freezing temperatures.

Mulching can help insulate the roots of Rosemary during colder months.

Instantly identify plants with a snap

Snap a photo for instant plant ID, gaining quick insights on disease prevention, treatment, toxicity, care, uses, and symbolism, etc.

Download the App for Free

Understanding Rosemary's Frost Hardiness

When it comes to frost hardiness, Rosemary (Salvia rosmarinus) can handle a surprising amount of cold, though it’s not entirely impervious to winter's worst. Generally, this aromatic herb can withstand temperatures as low as -7°C (20°F). However, its survival greatly depends on how prolonged and severe the frost periods are. For those gardening in zones 8 and warmer, Rosemary can usually survive the winter outdoors without much extra care. In colder climates, understanding its frost hardiness is crucial for successful overwintering.

How to Prepare Rosemary for Winter

Pruning Tips for Rosemary

Preparing your Rosemary for winter starts with proper pruning. Trim the plant back by about one-third in late summer or early fall. This helps to reduce the size of the plant, making it more manageable and less likely to suffer from winter dieback. Avoid heavy pruning just before winter, as new growth can be more vulnerable to frost damage.

Watering Needs During Winter

Watering Rosemary in the winter requires a fine balance. The plant’s soil should be kept slightly moist, but not soggy. Overwatering can lead to root rot, especially in cold conditions. Reduce the watering frequency as the weather cools down, ensuring the soil dries out between waterings. It’s usually best to water in the morning to give the soil time to dry out during the day.

Soil and Mulching Techniques

Proper soil and mulching techniques are pivotal in winterizing Rosemary. Ensure that the soil around your plant is well-draining to prevent root rot. Adding a thick layer of mulch (around 5-7 cm or 2-3 inches) can help insulate the roots and maintain a more stable soil temperature. Materials like straw, shredded bark, or even leaves work well for this purpose.

Indoor Care for Rosemary in Winter

Choosing the Right Container

If you plan to bring your Rosemary indoors, choosing the right container is essential. A pot that’s at least 30 cm (12 inches) in diameter is usually sufficient. Ensure the container has good drainage holes to prevent waterlogging. Terra-cotta pots are a great option as they allow for faster evaporation of excess moisture.

Indoor Light Requirements

Once indoors, Rosemary needs ample light to thrive. Place it in a south-facing window where it can receive at least 6-8 hours of direct sunlight daily. If natural light is insufficient, consider supplementing with a full-spectrum grow light to meet its light requirements.

Maintaining Humidity Levels

Indoor environments, especially during winter, can become quite dry. Rosemary prefers a more humid atmosphere, so it's beneficial to maintain a humidity level of around 40-50%. A humidity tray or occasional misting can help. Alternatively, placing a humidifier near the plant can also maintain consistent humidity levels.

Common Issues When Overwintering Rosemary

Pests and Diseases

Pests such as spider mites and aphids can become a problem when Rosemary is overwintered indoors. Regularly inspect your plant and, if necessary, treat with insecticidal soap or a neem oil solution. Good air circulation also helps prevent fungal diseases.

Yellowing Leaves

Yellowing leaves on your Rosemary plant can be a sign of overwatering or inadequate light conditions. Make sure the soil is well-draining and adjust watering practices to prevent root rot. Positioning the plant in a location where it receives sufficient light can also mitigate this issue.

Preventing Root Rot

Root rot is a common issue for Rosemary during winter, particularly if the soil retains too much moisture. Ensure good drainage in both pots and garden beds. Use a well-draining potting mix and avoid waterlogged conditions to keep roots healthy throughout the winter.

Learn More About Rosemary