How to Grow Lemongrass from Seed

Lemongrass loves heat and has a long season, so most gardeners start it indoors rather than sowing outside. Sow seeds 6 to 8 weeks before your last expected spring frost. The seeds are slow and a little unpredictable, so starting early indoors gives them the warm, steady conditions they need.

Wait to move plants outdoors until all danger of frost has passed and nighttime temperatures stay reliably above 50 degrees. Lemongrass stalls in cold soil, so there is no rush. In warm regions like south Florida, the Texas Gulf Coast, coastal Southern California, and the Deep South, lemongrass is a true perennial you can leave in the ground to return bigger each year. Gardeners in the Midwest, New England, and the Pacific Northwest should treat it as an annual or grow it in a large pot that comes indoors before the first frost.

Fill trays or small pots with a light seed-starting mix and moisten it well. Sow the seeds shallow, about 1/4 inch deep, and barely cover them, since a little light seems to help them sprout. Set the trays somewhere warm, ideally 70 to 85 degrees, because bottom heat from a seedling mat speeds things up a lot. Keep the surface evenly moist but not soggy while you wait, which can take anywhere from 14 to 40 days.

Once seedlings have a few blades and outdoor nights are warm, harden them off over a week and transplant into full sun. Lemongrass wants rich, well-draining soil that stays reasonably moist, with a slightly acidic to neutral pH. Space plants 24 to 36 inches apart, because each one grows into a wide clump. In containers, give a single plant a pot of at least 5 gallons so the roots have room to spread.

Lemongrass is a grass, which means it drinks and feeds heavily. Water regularly so the soil never fully dries out, roughly 1 inch a week and more during heat waves or for plants in pots. A monthly dose of a nitrogen-rich fertilizer keeps the blades green and the clump pushing out new stalks. A layer of mulch helps hold moisture and keep the roots cool.

The clumps expand fast. Every couple of years you can dig one up in spring and split it into smaller divisions to share or replant. No staking is needed, but give each plant elbow room so air moves through the foliage.

In zones 9 and warmer, lemongrass overwinters outdoors, though you may want to cut it back and mulch it. In colder areas, dig up a clump before frost, pot it, trim the tops to about 6 inches, and keep it by a bright window where temperatures stay above 40 degrees. Water sparingly through winter and move it back outside once spring nights warm up.

Lemongrass is a big, thirsty grass, so pair it with plants that enjoy the same warm, sunny, well-watered conditions. - Basil: loves the same heat and sun, and the two fragrances pair naturally in both the garden and the kitchen. - Cilantro: another Southeast Asian kitchen staple that appreciates the light afternoon shade a tall clump can cast. - Mint: happy in the same moist soil, though it is best kept in its own pot so it does not take over. - Marigolds: easygoing, cheerful companions that draw beneficial insects to the herb bed. - Peppers: chilis and sweet peppers share the heat and water needs and round out the same dishes. Keep lemongrass away from lean, dry-loving herbs like rosemary and thyme, which want the opposite of its rich, moist soil.

You can start harvesting once the stalks are about 1/2 inch thick at the base and the plant is at least a foot tall, usually 3 to 4 months after transplanting. Harvest the outer, more mature stalks first and let the center keep growing. Grip a stalk low and twist and pull, or cut it right at ground level.

The prize is the tender, pale lower few inches and the white swollen base, which is what you slice, bruise, or mince for cooking. Save the tough green upper blades too, since they make a fragrant tea when steeped and strained. Wear gloves when you harvest, because the leaf edges are sharp enough to give you a small nick. Take stalks as you need them all season, and cut a bigger batch before your first frost. Lemongrass freezes beautifully, so you can stash trimmed stalks in a bag for winter cooking.

In the kitchen, lemongrass is a cornerstone of Thai, Vietnamese, and Indonesian cooking. The bruised or minced white base flavors curries, stir-fries, marinades, and brothy soups like tom yum, and the stalks and leaves steep into a bright, citrusy tea served hot or iced. Trimmed stalks freeze or dry well, so a summer harvest can season your cooking all year.

In the garden, the arching blue-green clumps look handsome in a big container on a patio or at the back of a sunny bed. Many gardeners plant lemongrass near seating areas simply to enjoy its fresh citrus scent when a hand or a breeze brushes the leaves.

• Slow, patchy germination: lemongrass seed is naturally slow and uneven. Keep the mix at 70 to 85 degrees on a heat mat, stay patient for up to 40 days, and sow a few extra seeds to be safe.
• Rust (orange flecks on the blades): improve airflow between plants, avoid watering over the leaves, and remove badly spotted foliage.
• Browning leaf tips: usually a sign of dry soil or cold air. Keep the soil evenly moist and shelter containers from cold wind.
• Spider mites on overwintering plants: indoor air is dry, so rinse the foliage, raise the humidity, and wipe the leaves with insecticidal soap if needed.