Start lemongrass seeds indoors 8 to 10 weeks before your last frost date

Lemongrass seeds need warmth and moisture to sprout, so indoor starting gives you the best chance of success. Fill a seed tray or small pots with seed-starting mix — not garden soil, which compacts and holds too much water. Moisten the mix before you plant, then press seeds onto the surface without burying them; lemongrass seeds need light to germinate.

Cover the tray with a humidity dome or plastic wrap and place it in a warm spot, ideally between 70 and 80 degrees Fahrenheit. A heat mat under the tray speeds germination. Check daily and mist if the surface begins to dry. Seeds typically sprout in 7 to 14 days. Once you see green shoots, remove the cover and move the tray to a bright window or under grow lights.

Keep seedlings moist but not waterlogged. When they reach 2 to 3 inches tall, thin them so each seedling has room to grow, or transplant the strongest ones into individual 4-inch pots. Seedlings are ready to move outdoors after your last frost date and once they have developed 3 to 4 true leaves.

Key Takeaways

  • Lemongrass seeds must be started indoors 8 to 10 weeks before your last frost date because they need consistent warmth and will not survive cold soil.
  • Seeds should be pressed onto moist seed-starting mix and left uncovered, since they require light to sprout.
  • Seedlings need bright light, consistent moisture, and temperatures between 70 and 80 degrees Fahrenheit to develop strong roots before transplanting.
  • Outdoor planting works best in full sun and well-draining soil, with spacing of 12 to 18 inches between plants.

Prepare soil and choose a planting location outdoors

Lemongrass thrives in full sun — at least 6 to 8 hours daily — and loose, well-draining soil. If your garden soil is heavy clay, amend it with compost or peat moss to improve drainage; lemongrass roots rot in standing water. Test your soil pH if you have the means; lemongrass tolerates a range from 5.5 to 7.5, so most garden soils work.

Space plants 12 to 18 inches apart. In cooler climates, grow lemongrass in containers so you can move them indoors before frost. Use a pot at least 12 inches deep with drainage holes and fill it with potting mix, not garden soil. Container-grown plants dry out faster, so check soil moisture every 2 to 3 days during the growing season.

Harden off seedlings before moving them outside

Seedlings started indoors are tender and will wilt or die if exposed to outdoor sun and wind all at once. Begin hardening off about a week before your transplant date by placing seedlings in a sheltered, shaded spot outdoors for 1 to 2 hours. Each day, gradually increase their time outside and their exposure to direct sun.

By the end of the week, seedlings should tolerate a full day in outdoor conditions. Watch the weather forecast and avoid transplanting during a cold snap or strong wind. If frost threatens after you plant, cover seedlings with row cloth or move containers under shelter.

Water and feed seedlings and young plants

Lemongrass needs consistent moisture while it is establishing, but not soggy soil. Water when the top inch of soil feels dry to your touch. Once plants are 6 to 8 inches tall and growing steadily, you can reduce watering frequency slightly — mature plants tolerate dry spells better than seedlings do.

Feed seedlings indoors with a diluted liquid fertilizer every 2 to 3 weeks once they develop their first true leaves. After transplanting outdoors, explore a balanced fertilizer — such as a 10-10-10 formula — every 4 to 6 weeks during the growing season. Container plants need more frequent feeding because water drains nutrients from the soil faster.

Thin seedlings to prevent overcrowding

When seedlings are 1 to 2 inches tall, they compete for light and nutrients if they are too close together. Thin by removing the weakest seedlings with scissors rather than pulling them out, which can disturb the roots of survivors. Space remaining seedlings so each has at least 1 inch of space on all sides.

If you want to save thinned seedlings, transplant them carefully into individual pots filled with moist seed-starting mix. Handle them by their leaves, not their stems, which bruise easily. Keep newly transplanted seedlings out of direct sun for a day or two while they recover.

Manage light and temperature for strong growth

Seedlings grown indoors need 14 to 16 hours of light daily to stay stocky and green. If your window does not provide enough light, use a grow light positioned 4 to 6 inches above the seedlings. Adjust the height as plants grow so the light stays at the same distance.

Keep indoor seedlings between 65 and 75 degrees Fahrenheit at night and slightly warmer during the day. Avoid placing trays near heating vents or cold windows, which create temperature swings that stress young plants. Once seedlings are hardened off and planted outdoors, they tolerate a wider range of temperatures, though growth slows below 50 degrees.

Harvest lemongrass and extend the growing season

Lemongrass is ready to harvest once plants reach 12 inches tall, usually 3 to 4 months after transplanting. Cut outer stalks at the base with a sharp knife, leaving inner stalks to continue growing. Regular harvesting encourages bushier growth and prevents plants from becoming woody.

In mild climates, lemongrass can overwinter outdoors in the ground. In colder regions, dig up plants before the first frost, pot them, and move them indoors to a sunny window. Water sparingly over winter — the soil should be barely moist. In spring, move plants back outdoors after the last frost date, or divide them and start new seedlings from the divisions.

Frequently Asked Questions

How long does it take lemongrass seeds to germinate?

Lemongrass seeds typically sprout within 7 to 14 days when kept at 70 to 80 degrees Fahrenheit in moist, well-lit conditions. Germination is slower in cooler temperatures, so a heat mat speeds the process. Check seeds daily and mist the surface if it begins to dry.

Can I direct-seed lemongrass outdoors instead of starting indoors?

Direct seeding outdoors is possible but risky in most climates because lemongrass seeds need warmth and consistent moisture that outdoor soil often cannot provide. Starting indoors gives you stronger plants and a longer harvest window. If you live in a warm climate with a long growing season, you can direct-seed after soil reaches 70 degrees, but indoor starting remains the more reliable method.

Why are my seedlings tall and spindly?

Spindly seedlings mean they are not getting enough light. Move the tray closer to a window or raise a grow light to within 4 to 6 inches of the plants. Seedlings also stretch when temperatures are too warm at night; lower the temperature to 65 to 70 degrees if possible. Thin crowded seedlings so each has room to grow.

Can lemongrass survive winter outdoors?

Lemongrass survives winter outdoors only in USDA zones 9 and warmer, where frost is rare or absent. In colder zones, dig up plants before the first frost, pot them, and bring them indoors to a sunny window. Water sparingly over winter and move them back outdoors in spring after the last frost date.

What should I do if seedlings develop yellow leaves?

Yellow leaves usually signal overwatering or poor drainage. Let the soil dry slightly between waterings and may support your seed-starting mix drains freely. If seedlings are in a tray without drainage holes, transplant them into pots with holes. Yellow leaves can also mean the seedlings need feeding; explore diluted liquid fertilizer every 2 to 3 weeks once they develop true leaves.