Lemongrass (Cymbopogon citratus) is a tropical plant native to India that has recently gained popularity in the United States. The herb adds a fresh, lemony taste to Mexican, Vietnamese and Thai cuisine and is also used medicinally to treat headaches, muscle cramps and rheumatism. Hardy to zone 9, the plant reaches heights of 9 feet in warm climates. In temperate gardens, the plant grows to 3 feet tall, but must be overwintered indoors or in a greenhouse. Finding seeds and potted plants is difficult in most temperate climates, but lemongrass stalks are available in ethnic markets or grocery stores.
Fill a pot or seed-starting trays with sterile starting mix. Lay seeds on the mix, spaced 2 inches apart and cover with a fine layer of starting mix. Water with a spray bottle until evenly moist, but not soaking. Cover with a layer of plastic wrap and keep in a warm place (70 to 75 degrees Fahrenheit) until the seeds germinate, which can take 21 to 40 days. Water every two to three days to keep the soil moist.
Plant lemongrass from nurseries outdoors in your garden after all chance of frost has passed or in pots with sterile potting mix. Choose a sunny location, as lemongrass needs six to eight hours of sunlight per day. Water lemongrass so soil is evenly moist, but not soggy.
Buy stalks of bright green, healthy lemongrass if you're unable to find seeds. Trim off any yellow or dried parts of the plant and place in a glass of water. Set the glass in a sunny window and replenish the water when low. Roots appear at the base of the stalks in two to three weeks. Plant the lemon stalks in a pot or directly in the garden.
Dig up and pot garden-grown lemongrass in the fall, four weeks before the first expected frost. Use sterile potting mix, not garden soil, and take care not to disturb the shallow roots. Trim the plant to a height of 6 inches with scissors. Move the plants to a cool, shady area of the garden for two weeks to acclimate them before bringing them indoors.
Place lemongrass on a sunny windowsill. Provide a grow light or fluorescent bulb if the plant seems spindly. Position the light 3 inches above the plant and leave the light on for 14 hours daily. Continue to water as needed to keep the soil evenly moist.
Fertilize lemongrass plants with a liquid fertilizer according to package directions every two weeks while the plant is actively growing. Unless you have a greenhouse, lemongrass will probably go dormant midwinter. When the leaves start to yellow and die, cut them to 2 inches high and place the plant in a cool place. Water every three weeks and don't fertilize. In early spring, you'll notice new growth. Place the lemongrass in a warm, sunny windowsill and water and fertilize as previously directed. Move the plant outdoors after the last chance of frost.