The fragrant herb Cymbopogon citratus, commonly known as lemongrass, is a tropical perennial prized for its strong citrus flavor in teas and Asian cuisine. While its origins suggest it is ill-suited for the Rocky Mountain climate, it can be successfully cultivated in Colorado. Growing lemongrass requires treating it as a seasonal annual or a container plant moved indoors for the winter. Year-round outdoor survival is not possible due to the extreme cold, requiring adaptation to the short growing season and harsh winters.
The Climate Challenge for Tropical Plants
Lemongrass is a tender perennial reliably hardy only in USDA Hardiness Zones 9 through 11. Its growth is stunted below 50°F and it is easily killed by hard frost or prolonged exposure below 40°F. Colorado’s climate presents a significant barrier, as the majority of the state falls into Zones 3 through 7. Urban areas like Denver are typically Zone 6a, while higher-elevation mountain towns can be as low as Zone 3 or 4. Successful cultivation depends entirely on monitoring local spring and fall frost dates, which define the very narrow window for outdoor growth.
Maximizing Outdoor Growth in the Short Season
To ensure a productive harvest, treat lemongrass as a fast-growing annual to maximize the short summer period. Do not move the plant outdoors until all danger of spring frost has passed and nighttime temperatures consistently remain above 60°F, often pushing planting into late May or early June. Planting too early risks cold shock and inhibits establishment.
Lemongrass requires full sun exposure, meaning a minimum of six hours of direct sunlight daily, to encourage robust stalk development and enhance its aromatic properties. The soil must be rich, well-draining, and amended with organic matter, such as compost, to support its rapid growth. During the summer, the plant needs consistent moisture; water deeply when the top inch of soil feels dry, but avoid overwatering to prevent potential root rot.
For the best results, grow lemongrass in a container, such as a pot at least 12 inches in diameter. Container gardening allows for easy transportation and management as the seasons change. Regular feeding every few weeks with a balanced, water-soluble fertilizer during the peak growing season will support the plant’s aggressive growth.
Essential Strategies for Overwintering Lemongrass
To maintain the plant year after year, transition it indoors before the first expected fall frost, typically when nighttime temperatures drop below 50°F in early to mid-September. Prepare the plant by thoroughly pruning the stalks back to six to twelve inches. This reduction in foliage minimizes potential pest issues and prepares the plant for a period of reduced light.
The indoor care regimen depends on whether the gardener wants the plant to go dormant or continue slow growth. For dormancy, place the potted plant in a cool, dimly lit area like a basement or garage, where temperatures remain consistently between 50°F and 60°F. Watering must be drastically reduced to once a month in this state, allowing the soil to dry out completely between applications.
Alternatively, for continued slow growth, place the container in a bright, south-facing window to receive maximum winter sunlight. Watering should still be reduced compared to summer, but the soil should not be allowed to dry out completely. Regardless of the method chosen, fertilizer should be withheld entirely during the winter months, allowing the plant to rest until it can be moved back outdoors the following spring.