Lemongrass (Cymbopogon citratus) is a tropical grass known for its bright, citrus-like fragrance and flavor, widely used in cooking and aromatherapy. This tender perennial thrives in hot, humid climates with long growing seasons. Its ability to survive the winter depends entirely on local climate and temperature conditions. Due to the plant’s sensitivity to cold, most gardeners must make specific preparations to ensure its survival through colder months.
Lemongrass Hardiness and Temperature Limits
Lemongrass is reliably perennial only in the warmest regions, specifically United States Department of Agriculture (USDA) Hardiness Zones 10 and 11, where temperatures rarely drop below freezing. In these frost-free zones, the plant merely slows its growth during winter, and the foliage remains mostly green while the root system continues to live.
In cooler climates (Zone 9 and below), lemongrass must be treated as an annual or protected. The plant is highly sensitive to cold; temperatures below 40°F (4°C) cause growth to slow dramatically and foliage to die back. A hard frost or prolonged period below 32°F (0°C) will kill the roots, preventing the plant from returning the following spring. Gardeners in colder zones often dig up the plant to maintain it as a perennial, protecting the root clump from lethal cold.
Transitioning Plants for Indoor Survival
To successfully preserve lemongrass, the transition indoors must begin before the first hard frost. Initiate the process when nighttime temperatures consistently drop below 50°F (10°C), signaling the end of the active growing season. This timing prevents the plant from entering a damaging dormancy while still in the ground.
The initial step requires significant pruning of the foliage, cutting the stalks back to six to twelve inches. If the lemongrass was planted in the ground, carefully dig it up, keeping the root ball intact. Large, mature clumps often need division into smaller sections using a sharp tool, as the grass can become woody at its center.
Repot each section or the entire clump into a container at least 12 inches in diameter, using a quality, well-draining potting mix. Before moving the plant inside, thoroughly inspect it for pests like aphids or spider mites, which can quickly infest an indoor environment. Treat the plant with insecticidal soap or a strong spray of water to ensure a clean transition.
Care and Storage During Winter Dormancy
Active Growth Storage
Maintenance requirements depend on whether the goal is to keep the plant actively growing or to induce true winter dormancy. To maintain growth, place the plant in a warm area, ideally above 60°F (16°C), near a south-facing window to maximize sunlight. The plant requires at least ten hours of light daily, often necessitating supplemental grow lights to prevent weak foliage. Watering frequency must be reduced from the summer schedule, but the soil should remain consistently moist, not waterlogged. Fertilization should be stopped or significantly reduced during this period.
Dormancy Storage
Alternatively, the plant can be stored in a state of true dormancy, requiring a cool, dark location like a basement or unheated garage. The ideal temperature range for cold storage is between 40°F and 50°F (4°C and 10°C), which keeps the plant alive without encouraging new growth. In this dormant state, the foliage will likely turn brown and die back, which is normal due to the lack of light and cool temperatures. Watering is minimal, occurring about once a month, with just enough moisture added to prevent the root ball from completely drying out.
Spring Transition
As spring approaches, the plant needs a gradual reintroduction to outdoor conditions to prevent shock. Once the risk of the last spring frost has passed and nighttime temperatures remain reliably above 40°F (4°C), the plant can begin the hardening-off process. This involves slowly increasing its exposure to direct sunlight and outdoor temperatures over a couple of weeks before it is fully transplanted back into the garden or left permanently outside.