Lemongrass is the tall, lemon-scented grass that turns a stir-fry or a pot of tea into something special — and in most of the United States it has to be started indoors, because it is a tropical plant with no tolerance for frost at all. Seed is the cheapest way to get it, and a single packet can produce a whole clump.
Lemongrass seed needs warmth to germinate and a long, hot season to grow into the thick stalks you cook with, so indoor sowing is not optional in cold and temperate zones — it is the whole strategy. This guide covers the heat and light it demands, the long indoor head start, and how to move it outside only once summer has truly arrived. Lemongrass is a start-indoors crop — its sowing method is "start indoors" — so the steps below are the standard route, not a workaround. A tray indoors gives you control over warmth, moisture and light that outdoor sowing cannot match. This crop is in the Poaceae family, needs full sun, and takes 90–120 days to reach maturity, so the timing below is built around those facts, not guesswork.
Lemongrass at a glance
| Growing factor | What lemongrass need |
|---|---|
| Days to germination | 10–21 |
| Sowing method | start indoors |
| Days to maturity | 90–120 |
| Soil pH | 6.0–7.0 |
| Spacing | 24–36 inches |
| Sun | full sun |
| Cold tolerance | tender |
When to start lemongrass seeds indoors
In Zones 3–6, start indoors 10–12 weeks before your last frost — lemongrass needs the longest head start of any herb here. In Zones 7–8, 8–10 weeks is enough. In Zones 9–10, start indoors in late winter and plant out once nights warm up. In frost-free Zones 11–13, sow any time; lemongrass is a perennial there. Check your local extension service for frost dates, or use our frost-date calculator and seed-starting calculator.
As a rule, work backwards from your last frost: sow indoors 10–12 weeks before it if you are starting indoors at all, and check the seed packet against the germination time of 10–21 days. Our seed-starting calculator does the backwards maths for you, and the germination-time calculator helps you plan around that 10–21-day window. If you are unsure of your zone, the hardiness-zone finder will confirm it.
What you need
a seed tray or pots with drainage holes, seed-starting mix, a heat mat and thermostat if you have one, a clear lid, a spray bottle, a strong grow light, and larger pots for potting on. Lemongrass grows fast once it starts, so have 4-inch pots ready — seedlings outgrow cells quickly.
You will also want a spray bottle or a watering can with a fine rose, and a notebook to record the sowing date — germination takes 10–21 days, and it is easy to forget when you sowed.
Step by step: starting lemongrass seeds indoors
- Fill your containers. Fill trays or pots with fresh, damp seed-starting mix — not garden soil, which is too heavy and can carry disease. Press it down lightly and level the surface.
- Sow the seed. Sow lemongrass seed shallowly in warm, damp seed-starting mix and keep the tray at 70–80°F — a heat mat underneath makes a real difference, because cool soil slows germination to a crawl. Germination takes 10–21 days. Keep the lid on until seedlings appear, then remove it for airflow. The seedlings look like blades of grass from the start, so label the tray — they are easy to mistake for weeds.
- Cover and label. Cover the tray with a clear lid or cling film to hold humidity, and label it with the crop and the date. Put it somewhere warm and bright, out of direct sun until seeds sprout.
- Wait for germination. Germination takes 10–21 days. Check the tray daily, mist the surface if it dries, and be patient — uneven germination is normal, especially for slow crops. Our germination-time calculator helps you track the window.
- Remove the cover. As soon as seedlings emerge, take the lid off. Good airflow from this point on is what prevents damping off.
- Give them light. Move the tray under a grow light or to your brightest window immediately — seedlings stretch within a day or two if the light is weak.
- Thin and pot on. Thin to one seedling per cell once they have two true leaves, snipping the extras rather than pulling them. Pot on into larger pots when roots show at the drainage holes, keeping the seedlings at the same depth.
- Feed lightly. Once seedlings have two sets of true leaves, feed with a half-strength liquid feed every week or two. Do not overfeed — soft, overfed seedlings are more likely to damp off and less likely to harden well.
Light for seedlings
Lemongrass is a full-sun tropical grass and its seedlings want as much light as you can give them: 14–16 hours a day under a grow light set a few inches above the leaves. A windowsill alone is rarely enough — without strong light the blades go pale and floppy. Our grow-light calculator helps you check your setup.
Watering seedlings
Lemongrass has moderate water needs but likes steady moisture while young. Keep the mix evenly damp, watering from below, and never let seedlings dry out completely — drought at this stage stunts them badly. Once plants are established outdoors they are tougher, but indoor seedlings need consistent watering. Our watering calculator can help you work out how much water your seedlings need as they grow.
Hardening off
Lemongrass is tender and hates cold wind as much as frost. Harden off over 10–14 days, starting with a few hours in warm, sheltered shade and building up to full sun. Do not put it out at all until nights are reliably warm — a single cold night can set it back weeks.
Transplanting outdoors
Wait until all frost danger has passed and night temperatures are reliably above 50°F. Plant in full sun, in rich, moist soil, spacing plants 24–36 inches apart — a mature clump gets large. Our plant-spacing calculator helps with the layout. In cold zones, grow it in a large pot you can bring indoors for winter. For the full picture — soil, feeding, pests and harvest — see our complete growing lemongrass guide.
Common problems and fixes
| Problem | Fix |
|---|---|
| Seeds do not germinate | The soil was too cool. Lemongrass needs warmth — use a heat mat and keep the tray at 70–80°F. Germination takes 10–21 days, so give it time. |
| Pale, floppy seedlings | Not enough light. Move the grow light closer and run it 14–16 hours a day. Thin to one seedling per cell so they are not competing. |
| Seedlings dry out and die | Lemongrass seedlings are thirsty. Water from below daily if the mix dries fast, and do not let the tray sit in a draughty spot. |
| Cutworms after transplanting | Cutworms chew young stems at soil level. A cardboard collar around each stem at planting time stops them. |
Seeds do not germinate
The soil was too cool. Lemongrass needs warmth — use a heat mat and keep the tray at 70–80°F. Germination takes 10–21 days, so give it time.
Pale, floppy seedlings
Not enough light. Move the grow light closer and run it 14–16 hours a day. Thin to one seedling per cell so they are not competing.
Seedlings dry out and die
Lemongrass seedlings are thirsty. Water from below daily if the mix dries fast, and do not let the tray sit in a draughty spot.
Good companions for lemongrass include tomatoes, peppers, marigolds, cabbage. Watch out for aphids, slugs, cutworms — check young plants regularly, and deal with pests early while plants are small. Our pest-identifier helper can help you work out what you are looking at.
Frequently asked questions
How long do lemongrass seeds take to germinate?
10–21 days in warm soil. A heat mat speeds things up noticeably — without one, germination is slow and patchy.
Can I grow lemongrass from seed in a cold climate?
Yes, as an annual: start indoors 10–12 weeks before your last frost, plant out after frost, and harvest before autumn frosts. Or grow it in a pot and bring it indoors for winter.
Why is my lemongrass seed not sprouting?
Usually the soil is too cool or too dry. Keep the mix warm and consistently damp, and make sure the seed is fresh — check old packets with our seed-viability checker.
How far apart should lemongrass plants be?
24–36 inches apart. Each plant becomes a large clump, so do not crowd them.
When can I harvest lemongrass?
About 90–120 days from sowing, once stalks are at least half an inch thick at the base. Cut the outer stalks and leave the centre to keep growing.