Lemongrass (Cymbopogon citratus) is an aromatic tropical grass prized for its distinctive citrus flavor. Because this herb originates in warm, humid climates, gardeners in temperate regions often question its survival. The U.S. Department of Agriculture (USDA) Plant Hardiness Zone Map categorizes regions based on the average annual extreme minimum winter temperature. For gardeners in Zone 7, the primary concern is whether this tropical perennial can withstand the local cold.
The Hardiness Verdict for Zone 7
Lemongrass is not a perennial in USDA Hardiness Zone 7; it will not survive the winter outdoors without protection. This tender perennial is naturally hardy only in tropical or subtropical areas (Zones 9 through 11). The survival threshold for Cymbopogon citratus is a minimum temperature of about 20°F (-6.7°C).
Zone 7 presents a challenge because its average annual extreme minimum temperature range falls between 0°F and 10°F (-17.8°C to -12.2°C). These temperatures are well below the plant’s tolerance level, ensuring the root system will freeze and die if left in the ground. Therefore, Zone 7 gardeners must treat lemongrass as a warm-season annual or bring the plant indoors to overwinter it.
Seasonal Cultivation Requirements
Since lemongrass will not survive the winter, successful growth in Zone 7 requires maximizing its performance during the active growing season. Planting should occur only after all danger of spring frost has passed, ideally when nighttime temperatures reliably remain above 60°F. This tropical grass thrives on heat and light, requiring a location that receives a minimum of six hours of direct, full sunlight daily.
Lemongrass prefers loose, rich, well-draining soil amended with organic matter. As a vigorous grass, Cymbopogon citratus is a heavy feeder that requires consistent moisture to support rapid growth. During warm months, it needs ample water, often requiring daily watering for container plants during hot weather. Regular feeding with a balanced liquid fertilizer, perhaps every two weeks for container plants, encourages maximum production of the aromatic stalks.
Overwintering Methods
To maintain lemongrass as a perennial in Zone 7, gardeners must move the plant indoors before the first autumn frost, or when evening temperatures consistently drop below 45°F. This protects the root crown from cold damage. There are two primary methods for successful indoor storage: maintaining the plant in a state of semi-dormancy or forcing complete dormancy.
Semi-Dormancy
For the semi-dormant approach, the plant is potted and kept actively growing indoors. Before moving it, trim the foliage back to a manageable height of about 6 to 12 inches. The pot must be placed in the sunniest possible location, such as a south-facing window, or under supplemental grow lights. During this indoor period, the plant’s metabolism slows down, so watering should be significantly reduced. Water only when the top inch of soil feels dry, and cease all fertilizer applications until spring.
Complete Dormancy
The second method involves storing the plant in a fully dormant state, similar to overwintering bulbs. The entire root ball is dug up, or a potted plant is prepared by cutting the stalks down severely to only a few inches. This trimmed plant is then stored in a cool, dark location, such as a basement or unheated garage, where temperatures remain stable between 50°F and 60°F.
Temperature stability is important; warmer temperatures encourage weak, etiolated growth, while colder temperatures risk freezing the roots. The goal is to keep the plant alive but not actively growing, requiring only minimal moisture. Water the stored plant sparingly throughout the winter, just enough to prevent the root crown from desiccating.