Lemongrass, Cymbopogon citratus, is a tender perennial grass native to tropical and subtropical regions of Asia. It thrives in long, hot growing seasons and is sensitive to cold temperatures. In non-tropical climates, where winter temperatures regularly drop below 40°F, lemongrass will not survive outdoors. To maintain the plant as a perennial and ensure a continuous supply of aromatic stalks, it must be brought inside and successfully overwintered. This is done either by keeping the plant actively growing indoors or by inducing a period of dormancy.
Preparing the Plant for Indoor Living
The transition indoors must begin before the first hard frost, typically when nighttime temperatures consistently fall below 50°F. Moving the plant inside when temperatures drop to 45°F is a safer practice to prevent cold shock. If the lemongrass is planted in the ground, carefully dig it up, divide it, and pot it into a container with adequate drainage holes.
Before bringing the plant inside, prune the foliage severely to manage its size. Cutting the stalks back to a height of about 6 to 8 inches makes the grass manageable for an indoor space. A thorough inspection for pests like spider mites or aphids is essential, and any infestations must be treated before entry. Cleaning the exterior of the pot also removes any lurking pests or debris.
Essential Indoor Care Requirements
If the goal is to keep the lemongrass actively growing throughout the winter, the indoor environment must mimic its native tropical conditions. The plant needs the brightest light source available, ideally a south-facing window providing several hours of direct sunlight daily. If natural light is insufficient, supplemental grow lights should ensure the plant receives at least ten hours of light daily to sustain active growth.
Typical indoor temperatures between 60°F and 70°F are suitable for maintaining growth, but the plant should be kept away from cold drafts or direct heat vents. Watering frequency must be significantly reduced compared to summer months to prevent root rot. Allow the top inch or two of soil to dry out completely between waterings, and cease all fertilization during the winter period.
Choosing Between Active Growth and Dormancy
Inducing winter dormancy is a practical choice if adequate indoor light or space is limited. This method involves cutting the entire plant back hard, leaving only a few inches of stubble above the soil line. The root ball is allowed to dry out slightly before being stored for the winter.
The dormant plant should be placed in a cool, dark location, such as a basement or cellar, where temperatures remain consistently above freezing, ideally between 40°F and 50°F. During dormancy, the plant requires minimal maintenance, needing only occasional watering—perhaps once a month—to keep the rhizomes from desiccating.
Returning Lemongrass Outdoors in Spring
Once the threat of the last expected frost has passed and nighttime temperatures are reliably above 50°F, the lemongrass can move back outside. If the plant was kept dormant, bring it into a brighter, warmer area and resume regular watering and fertilization to prompt new growth. For plants that were actively growing indoors, new growth should already be visible.
The spring transition requires “hardening off,” which slowly acclimatizes the plant to the harsher outdoor conditions of direct sun and wind. This process involves gradually exposing the plant to the outdoors for increasingly longer periods over a seven to ten-day stretch. Starting with just an hour or two of morning sun and shade, this slow reintroduction prevents the foliage from experiencing sun scorch or severe shock.