Herb · Poaceae
Lemongrass
Cymbopogon citratus
Fed with sun, water, and heat, the arching blue-green clump keeps swelling its pale, lemon-scented stalk bases for the kitchen all season.
Full sun
Every 2–4 days
50–95°F · 10–35°C
75–100 days
Overview
Lemongrass throws up a fountain of slim, arching blades in a cool blue-green, each one long and narrow with a fine point and edges sharp enough to catch a careless finger. At the base the blades gather into pale, swollen stalks, firm and tightly wrapped in layered sheaths, and these lemon-scented stalks are the part that flavors so much Southeast Asian cooking. The whole clump of arching blades can reach 3 to 6 feet, and a hand run through it releases a clean burst of fresh lemon.
It is a tropical grass to the core, with no armor against cold. In zones 9 to 11, where winters stay mild, the crown holds and the blades return year after year as a perennial. In colder places the same clump is grown as an annual or lifted into a pot and carried indoors before the first frost.
The plant asks for little beyond sun, warmth, and water to keep its blades stiff and upright. Kept moist and fed through the growing season, one small fan of shoots swells into a full clump of dense blades within a few months. Let it dry out or catch a frost, though, and the blades slump, brown, and lose their green sheen while the clump stalls.
Care
The short version: full sun, soil kept evenly moist and never bone dry, plenty of warmth, and a monthly feed through the growing season, with a move indoors before frost in cold climates.
Light
Lemongrass wants full sun, the more the better, and in a bright, open spot the blades stand stiff, upright, and a deep blue-green. It puts up with a little afternoon shade, but light shade thins the clump and drains the lemon scent from the stalks.
Water
Keep the soil evenly moist and never let the pot dry out fully, since this thirsty tropical grass drinks steadily. Water every 2 to 4 days in warm weather, more in heat or in a container, and mist the slender blades where the air runs dry.
Soil
Plant it in fertile, loamy soil that drains well yet holds moisture, with plenty of organic matter worked in. It is easygoing about acidity, taking anything from a pH of 5.0 to 7.5.
Temperature
It thrives across 50°F to 95°F (10°C to 35°C) and pushes the fastest new blades at the top end. Growth slows as it dips toward 50°F, and frost blackens and kills the plant outright.
Humidity
Coming from humid tropics, lemongrass likes the air on the damp side, around 50% to 80%. In dry climates or a heated room, mist the blades or set the pot on a humidity tray to keep the fine tips from browning.
Feeding
Lemongrass is a hungry grass that answers a monthly feed through spring and early fall with thick, fresh blades. Use a balanced soluble fertilizer on the higher side for nitrogen, which drives all that leafy growth.
Pruning
Trim off the dead or brown outer blades to keep the clump clean, and harvest the thick, pale outer stalks by cutting them at ground level. In cold climates, cut the foliage back before you bring the clump indoors for winter.
Repotting
Repot once a year and divide the clump every 1 to 2 years, since it fills a container fast. When roots circle the pot, heave the clump upward, or drain water straight through, it is time to split and refresh the soil.
Size & spacing
A mature clump stands 3 to 6 feet (90 to 180 cm) tall and spreads 24 to 35 inches (60 to 90 cm) across, a broad fan of arching blades. Give it that much room so air moves through the blades and the clump has space to bulk up.
When to plant
Lemongrass needs warmth from start to finish and its blades die at the first frost. Set divisions or rooted stalks out only after the last spring frost, once nights stay above 50°F (10°C), then cut the pale, thickened stalks once the clump fills in, about 3 to 4 months later. Dig or carry it indoors before cold weather returns.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: After the last spring frost, once soil and nights are warm (above about 10°C / 50°F)
- Harvest: Rarely flowers in cool climates; harvest the thickened stalks once the clump is established, about 3-4 months after planting
Hardiness
USDA hardiness zones: 9–11
Temperature: down to -7°C
Troubleshooting
Most lemongrass trouble writes itself on the blades first, whether the browning comes from dry air, a rusty fungus, or a cold snap. Read the color and texture of the early damage and you can step in before a whole clump goes down. Match what you see below, then act while it still helps.
Tall blades slumped and browned the morning after a frost
The tall blades slump and turn a dull tan when cold hits, since lemongrass is frost-tender and starts to suffer below about 50°F (10°C). Foliage that wilts and browns in the hours after a cold night gives the cold away rather than any disease. Potted plants moved indoors before frost, the collapsed blades cut away, and a warm, bright spot bring fresh green growth by spring.
Fix:
- Move potted plants indoors before frost
- Cut back damaged foliage and overwinter the clump in a warm, bright spot
A knotted root mass heaving the clump up out of fast-drying soil
A fast-growing clump crams the pot with pale roots until it turns rootbound, leaving barely a skin of soil to hold water between them. Water drains through in seconds and the whole knotted clump heaves up above the rim. Splitting it into fresh soil or shifting it to a wider pot sets the blades pushing new growth again.
Fix:
- Divide the clump and repot into fresh soil
- Move up to a larger container
Papery tan tips and browned margins creeping down the blades
The narrow blades go papery and tan at their pointed tips first, and the browning creeps down the thin edges, since lemongrass comes from humid tropics and wants 50% to 80% humidity around it. A pot left to dry between waterings crisps them the same way, and a chalky crust of fertilizer salt burns the margins to a scorched line. Steady moisture, a misting in dry weather, and an occasional flush of the pot keep the blades green to their edges.
Fix:
- Keep soil evenly moist
- Raise humidity or mist regularly in dry climates
- Flush the soil to remove salts and reduce feeding
Rusty, raised specks stippling the length of each blade
Raised specks in rusty orange to brown stipple the length of the blades, the mark of rust, a fungus that takes hold when the leaves stay wet and the clump packs too dense for air to slip through. Drag a finger across a blade and the powdery spots smear off in a colored streak. Pulling the stippled leaves, thinning the clump, and watering at the base leave the foliage clean again.
Fix:
- Remove and destroy affected leaves
- Improve air circulation around the clump
- Water at the base rather than overhead
Toxicity
Lemongrass is a safe, much-loved cooking herb for people, but the blades tell a different story for pets. The ASPCA lists it as toxic to cats, dogs, and horses, since the essential oils and cyanogenic glycosides steeped in the grass upset the stomach. Cats need the closest watching, both because they handle the oils poorly and because a big mouthful of the tough, stringy blades can, in rare cases, knot into a blockage.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Mild
The citral oils packed into the blades usually leave a cat drooling, vomiting, and off its food. Cats break those oils down poorly, so concentrated lemongrass oil hits them hardest, and a mouthful of the stringy, tough-fibered grass can, in rare cases, knot up into a blockage.
Dogs Mild
A dog that chews the slim leaves or stems usually comes away with only a mild stomach upset, a little vomiting or a loose stool that clears on its own.
Horses Mild
A horse grazing the coarse grass may feel a mild bout of stomach upset and little else at the small amounts most would crop.
Rabbits Mild
The same essential oils that trouble cats and dogs can unsettle a rabbit's delicate gut, so the blades belong as a rare nibble rather than a regular green.
Livestock Caution
Grazing animals crop a little of the foliage without trouble, but the cyanogenic glycosides pile up in quantity, so a large feed of the blades is the part to watch.
Birds Caution
Birds are sensitive to plant oils, and the citral steeped in the blades may not sit well, so pet birds are best kept clear of the leaves.
People Culinary herb safe
Lemongrass is a kitchen staple, and the pale, tender swollen stalk bases are safe to cook and eat. The upper blades are simply too tough and fibrous to chew rather than poisonous, so they are trimmed away for flavor, not for safety.
Small culinary amounts of the stalk are typically low risk; concentrated lemongrass essential oil is the bigger hazard, especially for cats, which do not metabolize the oils well.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
United Kingdom
Animal PoisonLine: 01202 509000 (fee applies)
Australia
Animal Poisons Helpline: 1300 869 738
Varieties
Lemongrass is grown almost entirely as one culinary type, the blue-green clump you find in the kitchen and the garden center.
West Indian lemongrass
The standard culinary type carries slim blue-green blades above swollen, lemon-scented stalk bases that you cook with, and because it seldom sets seed it is grown from divisions rather than seed.
How to propagate
Lemongrass is among the easiest plants to multiply, whether you split a fan of blades from a clump you grow or root a bare stalk from the grocery store.
DivisionEasy
Spring, once growth resumes and temperatures are warm · 2-4 weeks to root and resume active growth
A mature clump lifted in spring pulls apart into fans of blades that each hold a knot of roots and a cluster of shoots, replanted straight away. Within 2 to 4 weeks they root in and send up new blades. Rooted grocery-store stalks, stood in water until white roots thread out from the base, pot up the same way.
Myths
A grass mild enough to flavor soup must be harmless to the animals of the house.
The ASPCA lists lemongrass as toxic to cats, dogs, and horses, and chewing the oil-rich blades brings on stomach upset. Concentrated lemongrass oil is the real danger, especially for cats, whose bodies cannot break the oils down well.
A thick, grassy clump like this is rugged enough to stand outside all winter.
It is a frost-tender tropical whose blades survive outdoors only in zones 9 to 11. Anywhere colder, grow it as an annual or dig the clump and keep it indoors until the weather warms.