Thyme

Light and exposure

Thyme wants full sun, no compromise. It is a scrubland plant, it needs the warmest and brightest spot in the garden to concentrate its aromas and stay compact. In the shade it runs up, goes bare and loses its fragrance.

Reserve for it a bank, a rockery, the edge of a path or a large pot placed where the sun strikes from the middle to the end of the day. The warmer and drier the spot, the better it fares. In a damp climate, this maximum sun exposure also helps the foliage dry quickly after the rains.

Watering

Thyme fears an excess of water far more than drought. Once established, it does almost without watering in open ground, except during long spells of great heat. A thyme that yellows and rots at the base almost always suffers from soil that is too wet.

In a pot, let the substrate dry well between two waterings and water sparingly. It is the opposite of most aromatics: here, too much water kills, not too little. In winter, do not water it, the rain is amply enough and the risk is rather one of excess.

Soil and repotting

Drainage is the absolute key for thyme, in any climate. It needs a poor, light, stony or sandy soil where water never stagnates. Heavy, clayey ground, waterlogged all winter, makes it rot for sure.

If your soil is heavy, plant the thyme on a mound, mix in gravel or coarse sand, or grow it in a pot with a lightened potting soil and a good drainage layer at the bottom. Avoid any excess of compost: thyme gives the best of its fragrance in a lean soil, a soil that is too rich makes it soft and bland.

Temperature and humidity

Common thyme is hardy down to about minus fifteen degrees Celsius, USDA zone 7, and withstands harder frosts still when the soil is dry. It is therefore not the frost that threatens it but the moisture: a mild, soaked winter is more fatal to it than a cold, dry one. The pairing of cold plus waterlogged soil rots the roots.

In practice, a well-drained thyme gets through the winter outdoors without protection. The useful gesture is not to cover it against the cold but to ensure that its feet are not sitting in water. In a pot, set it against a wall and raise the container on blocks so the water drains off freely and does not freeze in a solid block around the roots. This is a point that sets thyme apart from cool-climate herbs: it is protected from water, not from frost. Sudden thaws followed by a fresh freeze are more dangerous to it than a stable cold spell.

Pruning and upkeep

Prune the thyme every year after flowering, at the start of summer, cutting the stems back by about a third without ever cutting into the bare old wood, which does not restart. This pruning keeps the plant compact and bushy and delays its ageing.

An unpruned thyme goes bare in the centre, turns woody and lies down over the years. A light but regular pruning clearly prolongs its lifespan. Avoid pruning in autumn: the fresh stems would not have time to ripen their wood before the damp winter and would rot.

Pests and diseases

Thyme is little prone to disease when well planted in dry conditions. Its main enemy is not a pest but root and crown rot, caused by soil that is too wet in winter. A plant that blackens and dries out in patches is almost always the victim of an excess of water, not of a parasite.

In poorly drained soil, fungi of the Phytophthora type can attack the crown and the roots. Prevention is always the same: drainage, sunny exposure and measured watering. A thyme grown in the right conditions stays healthy without any treatment for years.

Propagation

Thyme propagates easily by cuttings and by division. In spring or summer, take semi-woody stem cuttings of five to eight centimetres, remove the lower leaves and plant them in a sandy mix kept just moist. Rooting takes a few weeks.

Layering is even simpler: bend a low stem to the ground, cover it with a little soil while leaving the tip out, it roots on its own and then separates from the mother plant. Sowing is possible in spring but slow and less true to type. Dividing or taking cuttings from an ageing plant lets you renew it before it goes bare.

Month-by-month care calendar

Green Hub tips

• Drainage above all: under a mild, rainy winter it is the stagnant moisture that kills thyme, never the cold.
• If your soil is heavy and clayey, grow the thyme in a raised pot or on a gravel mound. It hates wet feet.
• Prune after flowering, never in autumn, and without cutting into the bare old wood that does not grow back.
• Do not add compost: thyme gives its most intense fragrance in a poor, lean soil, a rich soil makes it bland.