Lemongrass is a tropical perennial grass, native to warm regions, and is prized for its intense citrus scent and flavor. Because it requires a long, hot growing season to produce the thick, usable stalks, gardeners in temperate climates must treat it as an annual. Starting lemongrass from seed indoors is the most reliable way to achieve a mature, harvestable plant within a single season, effectively extending the growing window.
Timing the Indoor Sowing
The time to begin sowing lemongrass seeds indoors centers around your region’s average last spring frost date. To give the tropical grass a significant head start, the ideal window for indoor sowing is typically eight to ten weeks before this final frost event. Starting the seeds this far in advance ensures the seedlings have enough time to develop into robust, stable plants.
Starting seeds too early, however, can lead to leggy, weak growth as the seedlings compete for light under artificial conditions for too long. For the best results, consult local agricultural resources to pinpoint your expected last frost date and then count back the appropriate number of weeks.
The ultimate goal of this timing is to prepare the seedlings for transplanting when the soil outdoors has warmed sufficiently. Lemongrass is highly sensitive to cold, so the soil temperature must be consistently warm, ideally above 60°F (15°C), before the plants can be set out permanently.
Essential Requirements for Seed Germination
Successful germination of lemongrass seeds relies heavily on providing consistent, tropical-like warmth. Lemongrass seeds require a minimum temperature of 68°F (20°C) to break dormancy, but optimal germination occurs within a sustained range of 70°F to 80°F (21°C to 27°C). Achieving this warmth usually necessitates the use of a heated seedling mat placed beneath the planting tray, providing the necessary bottom heat for the root zone.
When sowing, use a fine, sterile seed-starting mix in shallow containers or trays to prevent fungal diseases and ensure good drainage. Lemongrass seeds are considered light-dependent germinators, meaning they should be sown lightly on the surface of the soil rather than buried deeply.
Maintaining consistent moisture and high relative humidity is also necessary until the seeds sprout, which typically takes between seven and 14 days. Covering the seed tray with a clear plastic dome or plastic wrap traps moisture and creates a humid microclimate, but you must remove the covering immediately once the first shoots emerge to prevent dampening-off disease. Once the seeds have germinated, they require immediate and adequate light, such as a strong, full-spectrum LED or fluorescent grow light, positioned just inches above the seedlings to prevent them from stretching and becoming spindly.
Hardening Off and Transplanting Outdoors
Hardening off is a gradual, two-week process that slowly acclimates the plants to direct sun, wind, and cooler temperatures, preventing severe transplant shock. This process should begin about one to two weeks before the planned outdoor planting date, which is after all danger of frost is past.
Start by placing the seedlings outdoors in a protected, shaded location for just one to two hours on the first day, ensuring they are sheltered from any strong winds. Each subsequent day, increase the amount of time they spend outside by an hour or two, while also gradually exposing them to more direct sunlight.
Final transplanting should only occur once the nighttime temperatures are reliably staying above 50°F (10°C). The seedlings, now hardened and around three to four inches tall, should be planted in a location that receives full sun. If planting multiple clumps, space them about eight to twelve inches apart to allow for mature growth. After transplanting, water the seedlings thoroughly to settle the soil around the roots, and maintain consistent soil moisture during the initial establishment phase outdoors.