Rosemary is the hardest common herb to start from seed: germination takes 14–28 days, rates are low, and seedlings grow slowly for months. Most gardeners start rosemary from cuttings instead — but if you want a variety you cannot buy as a plant, seed is the way in, and patience is the price.

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

Rosemary at a glance

Growing factor What this crop needs
Days to germination 14–28
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 Rosemary seeds indoors

Start Rosemary indoors 8–10 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 rosemary seed indoors 8–10 weeks before your last frost — it needs the long lead time because germination takes 14–28 days and early growth is slow. In Zones 3–5, rosemary is usually grown as a potted plant brought indoors for winter; in Zones 6–7 it may survive mild winters with protection; in Zones 8–9 it grows outdoors year-round; in frost-free Zones 10–13 it becomes a woody shrub. It is tender when young, so keep seedlings warm and never plant out before frosts are past. Ask your local extension service about winter survival in your zone.

Zones 3–5: count back 8–10 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 24–36-inch spacing. Check old packets with the seed-viability checker.

Step by step: starting Rosemary seeds indoors

Rosemary is a start-indoors crop — sown under cover, grown into sturdy transplants, and planted out once the weather is right.

  1. Fill your containers. Use cell trays or small pots of fine, sterile seed-starting mix, dampened before sowing — not garden soil.
  2. Sow at the right depth. Sow seed barely covered — rosemary seed is tiny and needs light, two seeds per cell, thinning to the strongest later. Cheap insurance against a dud seed.
  3. Keep them warm. Rosemary germinates in 14–28 days, but only if the compost is warm. A heat mat or warm spot makes a real difference — cold compost is the commonest reason seed fails.
  4. Cover to hold moisture. Put a clear lid or cling film over the tray until sprouts appear, then ventilate daily and remove it within a day or two. Stale, wet air is where damping off starts.
  5. Light from day one. The moment seedlings emerge, move them under a grow light 2–4 inches above, or to the brightest windowsill, rotating trays daily. Leggy seedlings are almost always a light problem.
  6. Thin to one per cell. Snip the weaker seedling at soil level. Pulling disturbs the roots of the one you keep.
  7. Pot on when ready. Once seedlings have two sets of true leaves and roots show at the drainage holes, move them into slightly larger pots and start a quarter-strength feed once a week.
  8. Harden off before planting out. See below — skipping it is the single biggest cause of transplant losses.

Check old seed first with the seed-viability checker — a damp-paper-towel test saves a tray of wasted weeks.

Light for seedlings

Light separates stocky seedlings from leggy ones. Give Rosemary 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 Rosemary 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. Rosemary is tender — no frost tolerance at all, and even a light chill can check growth. 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 24–36 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 Rosemary 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 Low viability or cold seed Sow thickly, keep warm, wait a full 28 days.
Seedlings rotting Overwatering Let compost dry between waterings; rosemary wants low water.
Slow growth Normal for rosemary Be patient — growth speeds up once plants are established.
Leggy seedlings Too little light Strong light, 2–4 inches above; pinch to encourage branching.

No germination

Low viability or cold seed is the usual culprit. Sow thickly, keep warm, wait a full 28 days. If badly affected, re-sow — a fresh sowing usually overtakes a struggling seedling within two weeks.

Seedlings rotting

Overwatering is the usual culprit. Let compost dry between waterings; rosemary wants low water. If badly affected, re-sow — a fresh sowing usually overtakes a struggling seedling within two weeks.

Slow growth

Normal for rosemary is the usual culprit. Be patient — growth speeds up once plants are established. If badly affected, re-sow — a fresh sowing usually overtakes a struggling seedling within two weeks.

Frequently asked questions

Why is my rosemary seed not germinating?

It is slow and unreliable — 14–28 days and often low rates. Sow more seed than you need, keep it warm, and do not give up before four weeks.

Is it better to grow rosemary from cuttings?

Yes, for most people — cuttings root in weeks and are identical to the parent. Seed is for varieties you cannot get as plants.

How long does rosemary take to grow?

About 90–120 days to a small plant, and a year or more to a proper bush. It is a long game.

Does rosemary need a lot of water?

No — it has low water needs and hates wet feet. Let compost dry between waterings; overwatering kills more rosemary than drought.

Can rosemary survive winter outdoors?

In Zones 8 and above, usually yes. In colder zones, grow it in a pot and bring it inside before frost.

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