Growing Thyme from Seed: Germination and Handling Seedlings

Sow on the surface and do not bury it

Thyme seed is extremely small, roughly the size of ground pepper, and it needs light to germinate. Cover it and most of it will not come up at all. Sow on the surface of a firmed, gritty seed-starting mix, press it down with a flat hand or a piece of board so each seed sits in contact with damp compost, and leave it uncovered or add no more than the very lightest dusting of vermiculite.

Sow more thinly than feels natural. A pinch of thyme seed is hundreds of seeds, and a dense sowing gives you a mat of seedlings so fine that they cannot be separated without destroying them. Mixing the seed with a spoonful of dry sand makes it far easier to scatter evenly.

1. Use a gritty, low-nutrient compost Half seed-starting mix, half fine grit or perlite. A rich, water-retentive mix keeps the surface wet and rots the seedlings at the stem base.
2. Firm the surface before sowing Press the compost flat first. Seed that falls into hollows ends up buried by watering and does not come up.
3. Scatter thinly with sand Mix the seed into a spoonful of dry sand and sprinkle. You want seeds about a quarter inch (5 mm) apart, not a carpet.
4. Water from below only Stand the tray in shallow water until the surface darkens, then take it out. Watering from above washes surface-sown seed into a corner.

Sow in late winter or early spring under cover. Direct sowing outdoors works in warm regions but the seedlings are so small and slow that weeds usually beat them.

Warmth, patience and uneven germination

Thyme germinates at 65 to 70F (18 to 21C) and takes one to four weeks. It is genuinely erratic: some seeds appear in a week, others three weeks later, and germination rates are often only about half even with fresh seed. That is normal and does not mean the seed was bad or the sowing was wrong.

Because of that spread, do not give up on a tray early and do not throw it out at two weeks. Keep it warm, keep the surface just damp, and keep it in good light from the moment the first seedlings appear. Bottom heat from a propagator mat shortens and evens out the whole process noticeably.

Seed keeps around three years in a cool, dry, dark place. Older packets still work but sow them more thickly and expect fewer seedlings.

Damping off is the main risk

Thyme seedlings are tiny and the thing most likely to kill them is damping off, a fungal collapse at soil level that topples apparently healthy seedlings overnight and spreads across a tray in days. It is driven by a wet surface, still air and crowding, which is exactly what a covered propagator produces if it is never opened.

Prevention is the only treatment. Sow thinly, use clean trays and fresh compost, ventilate every day, let the surface dry very slightly between waterings, and always water from below. Once a patch has collapsed, remove those seedlings and the compost around them immediately and increase the airflow.

1. Ventilate daily Take the lid off for a while every day or prop it open. Standing condensation on the inside of the lid means the tray is too wet.
2. Let the surface dry slightly The compost should be damp below and just drying on top. Keep the surface glistening wet and you will lose the tray.
3. Thin early rather than late Snip surplus seedlings off at the base with scissors rather than pulling, which disturbs the roots of the ones you are keeping.
4. Do not feed seedlings Thyme seedlings need nothing until they are potted up. Feeding a tray of tiny seedlings gives soft growth that damps off more readily.

Reused trays are the usual source. Wash and dry them properly before sowing rather than tipping fresh compost into last year's tray.

Transplanting seedlings and growing on

Thyme seedlings stay minute for a long time. Wait until they have two or three pairs of true leaves and are big enough to hold by a leaf, which is usually four to six weeks after germination. Handle them by a leaf and never by the stem, since a crushed stem on a seedling this size is fatal.

Lift a clump with the point of a pencil or a dibber, tease individual seedlings apart and pot them singly, or in threes to a small pot if they are too small to separate, into a free-draining compost. Grow them on in good light and cool, airy conditions rather than pushing them with warmth, which gives soft plants that struggle outside.

1. Transplant at two or three true leaf pairs Into three and a half inch (9 cm) pots of gritty potting mix. Set each seedling at the same depth it was growing; burying the stem invites rot.
2. Harden off over a week or two Stand them outside during the day and bring them in at night for a week or more before planting out. Straight from a windowsill to a bed, they scorch and check.
3. Plant out after the last frost Plant 12 inches (30 cm) apart with the crown proud of the soil once frosts have passed and the soil is warm. Water weekly for the first month, then leave them.
4. Do not harvest in the first season Take almost nothing in the first year. Let the plant build a root system and a framework, and clip lightly instead to make it branch.

Seed-raised thyme is variable in scent, leaf size and habit. If one seedling turns out noticeably better than the rest, take cuttings from it, because that is the only way to keep it.

When seed is worth it and when it is not

Growing from seed makes sense when you want quantity, for a hedge, an edging or a large patch, and are happy with common thyme in its ordinary form. It is cheap and one packet plants a bed. It also takes a full season longer than any other method to reach a usable plant.

For a named variety, or where you want plants identical to one you already have, seed is the wrong tool: named thymes do not come true and many are sterile or barely set seed at all. A cutting or a layer gets you an exact copy in a fraction of the time.

Record the sowing date and how many seedlings you got from the packet. Germination varies enough between batches that your own note is worth more than the figure on the packet.