ThymeThymus vulgaris

Thyme wants what our climate offers least: sun all day and soil that does not hold water. Give it the warmest, driest spot in the garden, a south-facing bank, the top of a rockery, the summit of a herb spiral, the foot of a light-coloured wall, the edge of a paved terrace whose stones give back heat. Shun hollows, compact clays and the shade of trees, where it languishes and then rots in winter. Away from thirsty plants, it gets on well with rosemary, sage, lavender and strawberries.

Thyme grows in the garrigue: add neither compost nor manure, which would make it soft and scentless. In our loamy or clay soils, dig a hole 30 cm deep, mix the soil taken out with an equal volume of coarse sand, fine gravel or brick chippings, and raise the whole into a mound 10 to 15 cm above ground level. A handful of lime or wood ash reminds it of its native chalky soils. A layer of gravel on the surface, around the crown, will finish the job after planting by keeping moisture at bay.

Sowing is possible in March-April indoors, at 18 °C, in a seed tray of compost mixed half and half with sand; the tiny seeds are set on the surface and covered with a dusting of sand. Germination in two to three weeks, plants ready to go out in June, harvest the following year. Quicker and truer to type, cuttings are taken in June: take 8 cm non-flowering tips, strip the lower half of leaves, push them into a pot of damp sand under a plastic bag, in the shade; they root in three weeks. Layering a low branch, pegged down and covered with soil, is simpler still.

At the garden centre, choose a compact plant, branched from the base, with dense foliage and no bare stems, in a pot whose roots are not yet coming out. A tall, bare thyme, forced in a heated greenhouse, will establish badly. Rub a leaf: the scent should be strong. Common thyme, Thymus vulgaris, is the hardiest and the most useful in the kitchen; lemon thyme, a little less resistant, deserves a pot to bring under the eaves; creeping wild thyme carpets a rockery. A garden centre plant often divides into two or three at planting, which makes an edging at little cost.

Plant in April-May, when the soil is warming up, or in September to let autumn settle the roots before winter, every 30 cm. Make a hole in the prepared mound, remove from the pot, tease out circling roots, and set the plant so that the crown sits slightly above the soil. Fill in with the sandy mix, firm well and water only once, two litres, to settle it in. Then spread 2 cm of gravel or sand around the base. Young spring plants need weekly watering if it is dry until July, then nothing more.

A pot is often the best choice in Belgium, because it lets you keep thyme dry under the eaves or against a south-facing wall. Choose terracotta, which breathes, a pot of at least 20 cm, with a hole, and 5 cm of crocks or clay pebbles at the bottom. Fill with a mix of half potting compost and half coarse sand or lightened garden soil, without compost. No saucer. Water when the mix is dry right through, once a week in summer, almost never in winter. Repot every three years in March into a pot only slightly larger.

The most common is treating thyme like a vegetable: compost, rich potting mix, daily watering, a full saucer. It dies in one winter, drowned rather than frozen. The second is planting it in clay soil without lightening it, at ground level, in a damp corner. The third is letting a clump age without trimming, until it goes bare in the centre and no longer regrows. Finally, bringing thyme into the warm for winter makes it wither: it needs coolness and light, not heating. A pot under the eaves, outside, gets through winter far better than a kitchen.

A thyme established for a year is never watered again in open ground, even during our August heatwaves: its deep roots and tiny leaves are made for drought, and summer watering mainly encourages rot at the crown. Only the young plant, in its first season, gets a litre a week if the weather is dry. In a pot, wait until the mix is dry through its whole depth, lifting the pot to judge its weight: once a week in summer, once a month in winter, in the morning, without wetting the foliage. A grey, limp thyme has too much water, never too little.

The only mulch that suits thyme is mineral: gravel, coarse sand, slate chippings or volcanic grit 2 to 3 cm deep, which keep the crown dry, reflect heat and prevent soil splashes. Organic mulches, grass clippings, straw or leaves, hold moisture and rot it in winter. No fertiliser is needed; a fed thyme produces long, soft, scentless stems. At most, every two or three years in March, a handful of wood ash or lime at the base maintains the chalk it appreciates. Weed by hand, without deep hoeing, so as not to injure the shallow roots.

Trimming is the only care that matters. After flowering, in July, cut the whole clump back by a third with shears, in a rounded shape, always staying within the leafy parts: thyme does not regrow from bare old wood. A second light trim in September, without touching the wood, tightens the clump before winter. Never trim in late autumn or winter, as the wounds would freeze. Despite this care, a plant goes bare after five or six years: prepare its successors by taking a few tip cuttings every June, or layering the low branches, to replace old plants as you go.

Thyme has practically no pests, as its scent keeps them away. Its only real threat is rot of the roots and crown during our wet winters, prevented by the mound, the sand, the gravel and the total absence of compost. Foliage browning in patches in February signals excess water or heavy snow that stayed too long; cut out the dead parts in April and let it regrow. Slugs shun mature thyme but nibble cuttings. Mealybugs sometimes appear on a pot brought into the warm; a cotton bud dipped in alcohol or a spray of soft soap is enough.

March, removal of dead shoots, repotting if needed, a little lime. April-May, planting new plants, watering young plants only. June, flowering, visits from the bees, big harvest for drying just before the flowers open, cuttings for the next generation. July, trimming by a third after flowering. August, nothing, except picking. September, autumn planting, light shaping trim. October, moving pots under the eaves, on blocks. November to February, occasional picking in dry weather; a fleece laid over plants in open ground when a frost below -12 °C is forecast, removed as soon as it turns milder.

Pick all year round, with scissors, sprigs of 5 to 10 cm taken by working round the clump, never stripping one side or cutting down into the wood. The harvest for storing is done on a dry June morning, just before full flowering, when the essential oils are at their peak. In winter, thyme stays green and can be picked in dry weather, but reduce picking from December to February, as it does not regrow. Common thyme withstands -15 °C in drained soil; lemon thyme gives up around -8 °C and spends winter in a pot, under the eaves or in a bright, cold garage, watered once a month.