Thyme is a tiny-seed herb with outsized flavour: a single mature plant seasons a kitchen for years, and it asks for almost nothing — poor soil, little water, full sun. The seed is dust-fine, which makes sowing fiddly, but germination is reliable if you resist the urge to bury it.

It is best started indoors, under cover, and planted out once the weather is right.

Thyme at a glance

Growing factor What this crop needs
Days to germination 14–21
Sowing method both
Days to maturity 70–90
Soil pH 6.0–8.0
Spacing 9–12 inches
Sun full sun
Cold tolerance hardy

When to start Thyme seeds indoors

Start Thyme indoors 6–8 weeks before your last frost. Sow too early and you get leggy, root-bound plants; sow too late and you lose weeks of the season. Start thyme indoors 6–8 weeks before your last frost, surface-sowing the dust-fine seed onto moist compost. In Zones 3–5, transplant after frosts pass; in Zones 6–7 the same timing works, and plants establish fast in warm soil; in Zones 8–9 thyme grows year-round; in frost-free Zones 10–13 it is evergreen, though extreme heat can stress it — give afternoon shade. Thyme is hardy and drought-tolerant once established, so the indoor start is about getting plants going, not about frost protection. Your local extension service can advise on varieties for your climate.

Zones 3–5: count back 6–8 weeks from your last frost and sow under lights. Zones 6–7: the same lead time. Zones 8–9: the window opens earlier, and autumn sowing is often possible. Zones 10–13 are frost-free, so sow in the cooler months and let heat set the calendar. Use the frost-date calculator and the seed-starting calculator for your dates, and check your local extension service when in doubt.

What you need

You do not need much: fine, sterile seed-starting mix (not garden soil), cell trays or small pots, a tray to catch water, a spray bottle or fine watering can, labels and a marker, and a clear lid or cling film to hold humidity until germination. A grow light is the one item that transforms results — a sunny windowsill can work, but lights give stocky seedlings instead of leggy ones. The grow-light calculator helps size a light for your setup, and the seed-spacing calculator shows how many plants fit your beds at 9–12-inch spacing. Check old packets with the seed-viability checker.

Step by step: starting Thyme seeds indoors

Thyme can be direct-sown or started indoors — both work. Indoor starting wins when you want an earlier crop, even germination, or protection from slugs and cold soil.

  1. Fill your containers. Use cell trays, small pots or soil blocks of fine, sterile seed-starting mix — not garden soil, which is too heavy and can carry damping-off fungi. Dampen the mix before sowing.
  2. Sow at the right depth. Sow seed on the surface — thyme seed is dust-fine and needs light. Thyme germinates in 14–21 days, and depth matters — too deep and seed rots before it emerges.
  3. Label everything. Write the variety and date on every tray. In three weeks, when the trays look identical, you will be glad you did.
  4. Cover and keep moist. Cover with a clear lid or cling film to hold humidity. Ventilate daily once sprouts appear, and remove the cover within a day or two.
  5. Give light immediately. The moment seedlings emerge, move them under a grow light 2–4 inches above, or to the sunniest windowsill. Seedlings left in dim light go leggy within days.
  6. Thin to one per cell. Snip weaker seedlings at soil level rather than pulling them, which disturbs the keeper's roots. Final spacing outdoors is 9–12 inches.
  7. Feed lightly. Once true leaves appear, feed at quarter-strength once a week. Seed compost has almost no nutrients, and hungry seedlings turn yellow and stall.

You can also direct sow Thyme once soil is workable. Check old packets with the seed-viability checker.

Light for seedlings

Light separates stocky seedlings from leggy ones. Give Thyme seedlings 14–16 hours of light a day, with the source just 2–4 inches above the plants — raise it as they grow. A south-facing windowsill can work in spring, but turn trays daily or seedlings lean towards the glass, and on cloudy weeks even a good window is not enough. Our sunlight calculator tells you how much direct sun a spot gets, and the grow-light calculator helps size a light. If seedlings stretch, the light is not close or bright enough.

Watering seedlings

Seedlings want steady moisture, not wet feet. Water from below where possible — stand the tray in a shallow dish for ten minutes and let the compost wick it up — because overhead watering knocks tiny seedlings flat and keeps stems wet, which invites damping off. Check trays daily, since seed compost dries fast under lights, and Thyme has low water needs — they prefer to dry out between waterings, and overwatering is the bigger risk. Mist the surface lightly after sowing until germination, then switch to bottom watering. As transplanting approaches, let compost dry slightly more between waterings to toughen seedlings up.

Hardening off

Hardening off is the week that decides whether seedlings thrive or sulk. Over 7–10 days before transplanting, put trays outside for a few hours a day in a sheltered spot, increasing time, sun and wind exposure each day, and bring them back in at night. Start with shade and still air; end with a full day outside if temperatures allow. Seedlings that go straight from a warm room to open ground get sunscald, windburn or a cold check that sets them back for weeks. Thyme is hardy — it tolerates light frost, so it can go outside earlier than tender crops. Do not rush this step, and bring trays in if frost threatens.

Transplanting outdoors

Transplant on a cloudy day or in the evening, when the sun will not immediately stress seedlings. Water the trays an hour before, dig holes at the final spacing of 9–12 inches, and set each seedling at the same depth it was growing. Firm soil gently around the roots, water each plant in well, and mulch around (not against) the stems. Good companions for Thyme include tomatoes, peppers, marigolds, cabbage. Watch for aphids, spider mites, whiteflies in the first weeks — the pest-identifier helper can help name anything you find. Water daily for the first week while roots establish.

Common problems and fixes

Problem Likely cause Fix
No germination Seed buried Surface-sow; thyme seed needs light.
Damping off Wet compost Water from below; remove covers once sprouted.
Leggy seedlings Too little light Strong light close above; thin to one seedling per cell.
Seedlings rotting Overwatering Thyme wants low water — let compost dry between waterings.

No germination

Seed buried is the usual culprit. Surface-sow; thyme seed needs light. If badly affected, re-sow — a fresh sowing usually overtakes a struggling seedling within two weeks.

Damping off

Wet compost is the usual culprit. Water from below; remove covers once sprouted. If badly affected, re-sow — a fresh sowing usually overtakes a struggling seedling within two weeks.

Leggy seedlings

Too little light is the usual culprit. Strong light close above; thin to one seedling per cell. If badly affected, re-sow — a fresh sowing usually overtakes a struggling seedling within two weeks.

Frequently asked questions

How do you sow thyme seed?

On the surface — do not cover it. Mix the dust-fine seed with a little sand to spread it evenly, and mist to settle it in.

How long does thyme take to germinate?

About 14–21 days. Keep the surface moist but not wet — a clear cover helps until sprouts appear.

How long until thyme is ready to use?

About 70–90 days to a usable plant, and it improves with age — second-year thyme is far more productive.

Does thyme need rich soil?

No — it prefers poor, well-drained soil. Rich, wet soil makes leggy plants with weak flavour.

Can I grow thyme indoors?

Yes, on a sunny windowsill — it is one of the better herbs for indoor growing, as long as it gets strong light.

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