Common thyme

Identification and origin

Thymus vulgaris belongs to the mint family, Lamiaceae, alongside mint and rosemary. It is native to southwestern Europe: Spain, the Balearic Islands, France and Italy, where it grows on dry, rocky ground. Cultivated since ancient times, it has naturalized elsewhere, from Great Britain to New Zealand. Its name is thought to come from the Greek thymos, “perfume,” or thumos, “courage”; vulgaris means “common.”

It is an evergreen subshrub with a woody base, forming a dense mound 6–12 in tall and 6–16 in wide. Its square, finely hairy stems turn woody with age. The opposite leaves, 0–1 in long, linear to oval and dark gray-green, have edges rolled under. Highly aromatic they have a sweet, earthy, peppery flavor.

From late spring into early summer, small tubular, two-lipped flowers in white, pink or pale lilac open in whorls at the stem tips. Rich in nectar, they draw bees and butterflies.

It is sometimes confused with creeping thyme (Thymus serpyllum), which forms a lower mat; the upright mound of common thyme is easier to harvest. Common cultivars: ‘Argenteus’ and ‘Silver Posie’, with white-edged leaves; ‘Narrow Leaf French’, with fine gray leaves and a lighter flavor; ‘German Winter’, known for its winter hardiness; ‘Orange Balsam’, with an orange scent; and ‘Silver Queen’, silvery and lemon-scented.

Light

Thyme wants full sun: at least six hours of direct light a day. In shade it grows thin and spindly, its leaves get smaller and its aroma fades.

Indoors, set it against a south- or west-facing window. In winter, a full-spectrum grow light running twelve to sixteen hours a day, 6–12 in above the foliage, makes up for the missing light. Long, lanky stems are a sign that it needs more light.

Watering

Once established in the ground, thyme tolerates drought and almost never needs watering, except right after planting. Too much water is far more dangerous than too little: in soggy soil, especially in winter, the roots rot.

In containers, check more often in hot, dry weather. Water only when the mix is dry to the touch, before the plant wilts, then empty the saucer. Porous terracotta helps the mix dry out between waterings.

Indoors, keep the mix on the dry side. Heated winter air dries out the leaves: group pots together or set them on a tray of moist pebbles. On the other hand, air that is too humid and still encourages fungal problems; a small fan improves air movement.

Potting mix

In the garden it prefers light, sandy or rocky soil that drains perfectly, with a neutral to alkaline pH. In heavy soil that stays wet through winter, grow it in a container or a raised bed instead.

In a container, allow at least 6 in wide and 4 in deep for one plant, with plenty of drainage holes, and use a peat-free, soil-based mix with horticultural grit added, up to a quarter of the volume. In the garden, no fertilizer is needed. Indoors, a light dose of water-soluble fertilizer every two weeks is enough: feeding more often harms its flavor and fragrance.

Temperature

Common thyme is hardy in USDA zones 5a to 9b and withstands winters around 5–14 °F in well-drained soil. Winter wet, more than cold, is what kills it: cover plants in the ground with a cloche during very rainy winters and move pots near a wall, out of the rain. In a container, aim to keep it above 14 °F.

Indoors, it grows well between 61–70 °F, ideally 64–70 °F by day and 55–61 °F at night. Keep it away from heaters, which dry it out.

Repotting

Plant in the garden from mid-spring to early summer, 8–12 in apart and at the same depth as in the nursery pot. A plant raised indoors must first be gradually accustomed to full sun and wind.

In containers, repot when roots grow through the drainage hole, preferably in early spring. To enjoy it through winter, pot up a plant in fall, set it in front of a sunny window and move it back outdoors in late spring.

Pruning

Trim lightly after flowering, and in spring if needed, to keep the mound compact. Do not cut hard into old wood: the stems might not regrow. After a few years the plant becomes woody and bare in the center; it is then better to replace it with a cutting.

Harvesting doubles as pruning. Snip sprigs year-round; the flavor peaks just before flowering. Always leave 5 in of leafy stems, and never remove more than a third of the plant at once. To dry, hang bunches upside down in a dark, airy place. Both the young leaves and the flowers are edible.

Propagation

Cuttings are the most reliable method. In spring or early summer, take tips about 4 in long from new shoots, strip the lower leaves and insert them in sand kept moist. In summer, semi-ripe cuttings also work.

Layering is very simple: in spring or fall, pin a low stem against the soil. To divide, in spring or fall, dig up the root ball and split it into pieces that each carry roots.

Seed is slow and uneven. In spring, sow indoors on the surface of moist seed-starting mix, without covering, at 59–68 °F; germination takes about two weeks. Water sparingly to prevent damping off, then move seedlings to 3 in pots. Allow about a year before the first harvest. Seed from a named cultivar will not reliably match the parent plant.

Common problems

• Decline, a collapsing plant: root rot from poorly drained soil or too much watering, especially in winter.
• Spindly stems, small leaves, weak fragrance: too little light, common indoors.
• Bland flavor: too much fertilizer, or a plant allowed to flower indoors; snip the tips regularly.
• Bare, woody clump: an old plant, or one that was never trimmed.
• Young shoots eaten: slugs and snails.
• Chewed leaves or pale mottling: rosemary beetle, leafhoppers.
• Indoors: fungus gnats (yellow sticky traps, less frequent watering) and aphids (cut off infested sprigs).

A single symptom can have several causes: consider light, watering, drainage and the roots together before acting.

Toxicity

Common thyme is not considered toxic to dogs, cats or horses, and it is an edible culinary herb for people. If an animal eats a large amount or reacts unusually, ask a veterinarian for advice.