Lemongrass seeds need warmth, moisture, and light to sprout—start them indoors 6 to 8 weeks before your last spring frost

Lemongrass seeds are slow to germinate and need consistent warmth to break dormancy, so most gardeners start them indoors under grow lights or on a sunny windowsill rather than direct sowing outdoors. The seeds themselves are tiny and need light to sprout, which means you should press them into soil rather than cover them. Starting indoors gives you a head start on the growing season and lets you move seedlings outside once soil temperatures stay above 50°F.

The entire process from seed to transplant-ready seedling takes 8 to 12 weeks, so timing matters. If your last spring frost arrives in May, count backward and start seeds in late February or early March. Lemongrass is a tropical plant and will not tolerate cold soil or frost, so patience with the indoor phase pays off in stronger plants.

Key Takeaways

  • Lemongrass seeds need light to germinate, so press them into the soil surface rather than burying them, and keep them under grow lights or in a bright window.
  • Soil temperature should stay between 70°F and 80°F for seeds to sprout within 10 to 14 days; a heat mat under seed trays speeds germination significantly.
  • Start seeds indoors 6 to 8 weeks before your last spring frost date, then transplant seedlings outdoors only after soil has warmed and frost danger has passed.
  • Lemongrass seedlings grow slowly at first and need consistent moisture but not waterlogged soil; let the top of the soil dry slightly between waterings.

What you need before you start

Gather seed-starting mix (a sterile, lightweight blend designed for seeds, not garden soil), small pots or seed trays with drainage holes, lemongrass seeds, and a way to provide warmth and light. A heat mat designed for seed starting is not required but cuts germination time in half. If you do not have one, a warm spot like the top of a refrigerator or a heating vent works, though germination will be slower.

For light, a south-facing windowsill works if you have one, but a basic two-bulb fluorescent or LED grow light positioned 2 to 3 inches above the seedlings is more reliable. Lemongrass seedlings are leggy (tall and thin) without enough light, and a grow light prevents that. You will also need a spray bottle or watering can with a fine rose to keep soil moist without washing seeds away.

Filling containers and preparing the soil surface

Fill your pots or seed trays with moistened seed-starting mix until about half an inch from the rim. Press the mix down gently so it is firm but not compacted. The soil should be damp but not soggy before you place seeds—if water drips from a handful, it is too wet.

Lemongrass seeds are extremely small, so handle them carefully. Sprinkle seeds thinly across the soil surface, spacing them about half an inch apart if you are using individual pots, or scatter them in seed trays and thin seedlings later. Do not bury the seeds. Instead, press each seed gently into the soil with your finger or a pencil so it makes contact with the moisture below. The seed needs light to germinate, so leaving it on the surface is correct.

Providing heat and moisture for germination

Place seed trays on a heat mat set to 75°F, or in the warmest spot in your home. Cover the trays loosely with a humidity dome or clear plastic wrap to hold moisture in the air around the seeds. Check daily and mist the soil surface with a spray bottle if it begins to look dry on top—the goal is consistently moist, not waterlogged.

Germination usually takes 10 to 14 days at 70°F to 80°F, but can take three weeks or longer in cooler conditions. Be patient; lemongrass is not a fast starter. Once you see the first green shoots, remove the humidity dome and move the trays under grow lights or to a bright windowsill when ready. Seedlings that do not get light right away will stretch and weaken.

Light and watering after seedlings emerge

Position grow lights 2 to 3 inches above the seedlings and run them for 14 to 16 hours per day. If you are using a windowsill, rotate the trays every few days so seedlings grow straight rather than leaning toward the light. Water when the top half inch of soil feels dry to the touch—do not let the soil dry out completely, but do not keep it soggy either. Overwatered seedlings develop damping off, a fungal disease that kills them at the soil line.

Lemongrass seedlings grow slowly at first and may look fragile for several weeks. This is normal. Keep the soil consistently moist and the light on schedule, and the seedlings will gradually develop true leaves (the second set of leaves that look more like grass). Once seedlings have two or three sets of true leaves and are 2 to 3 inches tall, they are ready to thin or transplant into individual pots if they are crowded.

Hardening off before moving seedlings outdoors

About two weeks before your last spring frost date, begin hardening off the seedlings—gradually exposing them to outdoor conditions so they adjust to wind, direct sun, and temperature swings. Start by placing the trays outside in a sheltered, shaded spot for one to two hours on a mild day. Bring them back inside.

Over the next 10 to 14 days, increase outdoor time by an hour or two each day and gradually move them into brighter light. By the end of the hardening-off period, seedlings should spend the full day outside in dappled shade or morning sun. Bring them in at night until nighttime temperatures stay above 50°F consistently. This process prevents transplant shock and gives seedlings time to toughen up.

Transplanting into the garden or larger pots

Lemongrass grows best in warm soil, so wait until soil temperature reaches at least 60°F and preferably 70°F before planting outdoors. Space plants 18 to 24 inches apart in full sun and well-draining soil. If your garden soil is heavy clay, amend it with compost or sand to improve drainage—lemongrass does not tolerate wet feet.

If you live in a cold climate, grow lemongrass in a large pot (at least 12 inches wide) that you can move indoors before the first frost. Container-grown lemongrass needs more frequent watering than garden plants but gives you the option to overwinter it on a sunny windowsill. Water deeply after transplanting and keep the soil consistently moist for the first two weeks while roots establish.

Common problems and how to avoid them

Seeds that do not germinate are usually too cold or buried too deep. Lemongrass needs warmth and light, so a heat mat and grow light solve most germination failures. If seedlings look pale or yellow, they are not getting enough light or nutrients; move them closer to the light source or feed them with a diluted liquid fertilizer once they have true leaves.

Damping off—where seedlings collapse at the soil line—happens when soil stays too wet or air circulation is poor. Prevent it by watering only when the soil surface feels dry, removing the humidity dome as soon as seedlings emerge, and running a small fan on low speed near the trays to keep air moving. If damping off appears, remove affected seedlings when ready and let the soil dry out slightly between waterings.

Frequently Asked Questions

Can I direct sow lemongrass seeds outdoors instead of starting them indoors?

Direct sowing is possible in warm climates where soil stays above 70°F by late spring, but germination is slow and unreliable outdoors. Indoor starting gives you stronger plants and a longer growing season. If you do direct sow, press seeds into warm, moist soil in full sun and keep the area consistently moist until seedlings emerge.

How long does it take lemongrass to grow from seed to harvest?

Seedlings started indoors and transplanted outdoors in spring can reach harvestable size (12 to 18 inches tall) by mid to late summer, usually 4 to 6 months after planting seeds. You can harvest outer leaves once the plant is established, but wait until it is at least 12 inches tall before cutting heavily.

Do lemongrass seeds need to be soaked before planting?

Soaking is not required but can speed germination slightly. If you soak seeds, do so for 24 hours in room-temperature water, then drain and plant when ready. Do not soak longer than 24 hours or seeds may rot.

What temperature kills lemongrass seedlings?

Frost and temperatures below 50°F damage or kill lemongrass seedlings. Keep seedlings indoors until nighttime temperatures stay consistently above 50°F, and do not transplant outdoors until soil has warmed. If an unexpected frost is forecast after transplanting, cover plants with row cover or move potted plants indoors temporarily.

Can I save seeds from my lemongrass plant?

Lemongrass grown from seed in cold climates rarely flowers and sets seed before frost arrives. In tropical or subtropical regions where plants survive year-round, flowers appear in late summer and produce viable seeds, but seed saving is not practical for most home gardeners. It is easier to start new plants from seeds purchased from a seed company or propagate from cuttings of an established plant.