Lemongrass (Cymbopogon species) is a tropical perennial grass native to the warm climates of Southeast Asia. This heat-loving plant’s successful cultivation is highly dependent on environmental temperature. Understanding its specific temperature boundaries is the most important factor for gardeners attempting to grow it outside of its native, frost-free habitat.
Optimal Temperatures for Vigorous Growth
Lemongrass thrives when temperatures are consistently warm, requiring 70°F to 90°F (21°C to 32°C) for robust development. Within this thermal window, the plant engages in rapid and prolific growth, producing the thick, flavorful stalks desired for harvest. The warmth directly influences metabolic processes, optimizing photosynthesis and fueling the plant’s growth.
These conditions also promote the synthesis of aromatic compounds, like citral, which provide its distinctive scent and flavor. When temperatures are reliably high, the plant focuses energy on producing these volatile oils, resulting in a higher-quality yield. If a plant receives adequate moisture and sunlight but not enough heat, its growth will be noticeably stunted, and stalk production will be minimal.
Cold Tolerance and Survival Limits
As a tropical species, lemongrass has a low tolerance for cold; its survival limits are defined by freezing temperatures. When air temperatures dip consistently below 50°F (10°C), the plant’s growth slows dramatically, triggering a state of semi-dormancy. This physiological response is a survival mechanism, allowing it to conserve energy until warmer conditions return.
The lethal threshold is reached with frost or sustained freezing conditions, causing irreparable damage to the foliage and the root crown. Lemongrass is hardy only in USDA hardiness zones 9b through 12, where frost is rare. Exposure to temperatures below 32°F (0°C) will kill the plant outright, destroying the root structure necessary for perennial regrowth. Even temperatures below 40°F (4°C) can cause cold damage, resulting in browning or wilting leaves.
Practical Protection Strategies for Temperature Extremes
For gardeners in cooler climates (Zone 8 and below), overwintering strategies are necessary to preserve the plant. The most reliable method involves growing lemongrass in a container and moving it indoors before nighttime temperatures drop below 45°F (7°C). Once indoors, the plant should be placed in a cool, dimly lit location, such as a basement or garage, where temperatures remain between 50°F and 60°F.
During this induced dormancy, the plant requires minimal water—just enough to keep the root ball from completely drying out. Alternatively, in borderline zones like Zone 9, a heavy layer of mulch, about three inches deep, can be applied over the root crown to insulate it against potential cold snaps. The primary goal of these interventions is to protect the tender root system from the lethal effects of freezing soil.
Managing the plant during summer heat extremes is also important, particularly when temperatures exceed 95°F (35°C). While lemongrass is heat-tolerant, prolonged exposure to scorching sun can lead to leaf burn and wilting. During heatwaves, providing temporary afternoon shade using a shade cloth can prevent the leaves from drying out and succumbing to sunscald.
Consistent and deep watering becomes paramount during periods of high heat to prevent moisture stress. Potted plants are especially vulnerable to rapid drying and may require daily watering to maintain the moist soil conditions that lemongrass prefers. These measures ensure the plant remains hydrated and minimizes stress, allowing it to continue converting solar energy into flavorful stalks.