Winter presents a challenge to the survival of potted herbs, especially in regions that experience frost or extended cold. Containers offer less insulation for roots compared to the ground, making plants vulnerable to freezing temperatures. Successful winterizing requires shifting the location and changing maintenance practices to match the plant’s needs during reduced light and colder conditions. The goal is to either encourage continued, slower growth indoors or protect the plant while it enters a dormant phase.
Preparing Potted Herbs for the Cold Transition
Preparation begins well before the first hard frost, typically when nighttime temperatures drop into the 40s or 50s Fahrenheit, especially for tender herbs like basil. Stop fertilizing by late summer or early fall to discourage tender new growth that will not survive the cold. Take cuttings from desirable plants, like mint or rosemary, as a backup in case the parent plant does not survive the winter. Before bringing pots indoors, thorough pest inspection is required to avoid introducing pests like spider mites or aphids. A strong spray of water can dislodge many insects, and cleaning the pot’s exterior removes debris and potential insect eggs.
Assessing Herb Hardiness and Choosing the Winter Location
Winter care is determined by the herb’s hardiness, which separates herbs into three main groups. Tender annuals, such as basil, dill, and cilantro, cannot survive frost and must be moved indoors for active growth or allowed to die back. Tender perennials like rosemary, bay laurel, and pineapple sage also need protection from freezing. They are best moved to a cool, bright, semi-dormant location, ideally maintaining temperatures between 40 and 60 degrees Fahrenheit.
Hardy perennial herbs, including chives, mint, oregano, and thyme, are adapted to cold and benefit from a period of dormancy. These plants can often remain outdoors with added protection or be moved to an unheated space like a shed or garage. This prevents their roots from freezing solid inside a container. The chosen location dictates the subsequent care routine for the winter season.
Adjusting Care Routines for Indoor Herb Survival
Herbs brought indoors for continued growth, mainly tender annuals, require significant environmental adjustments. The primary challenge is light, as the intensity of a sunny winter windowsill is far less than summer sun, which can lead to “legginess,” or weak, stretched stems. A south-facing window is usually the best option, but supplemental light from a grow lamp is often required to provide the six or more hours of intense light necessary for healthy growth.
Indoor heating creates a warm, dry environment, so herbs should be kept away from direct heat sources like radiators and cold drafts. A consistent room temperature between 60 and 70 degrees Fahrenheit is tolerated by most active herbs. Watering practices must be reduced significantly to compensate for the plant’s slower growth rate and lack of air circulation. Overwatering is the leading cause of indoor herb death, as wet soil deprives roots of oxygen and encourages fungal root rot. Only water when the top inch or two of the potting mix feels dry to the touch.
Managing Outdoor Dormancy and Protection
Hardy perennial herbs remaining outside need protection to prevent their root systems from freezing and thawing repeatedly, which can heave plants out of the soil. Since container roots are exposed to air temperature, they are considered two hardiness zones less resilient than if planted in the ground. Insulation is achieved by grouping pots tightly together in a sheltered area, such as against a warm, south-facing house wall, which offers shared thermal mass.
Pots can be further insulated by wrapping the containers with materials like burlap, bubble wrap, or straw to create an air barrier, protecting the roots from rapid temperature swings. Another effective method involves burying the entire pot in the ground or mounding a thick layer of mulch, such as wood chips or straw, over the container and plant crown. Even dormant herbs require minimal moisture throughout winter to prevent desiccation. Check the soil every few weeks and provide a small amount of water if the soil is completely dry and the temperature is above 40 degrees Fahrenheit.