UK winters are rarely brutal, but they are unpredictable: a mild, wet December can lull tender herbs into soft growth, then a sharp frost in February finishes them off. Container herbs are especially vulnerable because their roots sit above ground, exposed to freezing air on all sides. With a little forethought now, though, you can carry basil, lemon verbena, French tarragon and other tender favourites through to spring.

Know Which Herbs Need Winter Help

Not every herb in a pot needs mollycoddling. Rosemary, thyme, sage, mint and chives are hardy enough to shrug off most UK winters, though they still dislike waterlogged compost. The ones to cosset are the truly tender types:

• Sweet basil, coriander, dill and chervil
• Lemon verbena and French tarragon
• Scented pelargoniums and Vietnamese coriander

These are the plants that turn to mush at the first hard frost. If you have a greenhouse, conservatory or bright windowsill, that is the simplest solution: move them under cover before the first frost is forecast. For everyone else, the techniques below will tip the odds in their favour.

Move Pots to a Sheltered Wall

Cold air is heavy and sinks, so the lowest part of the garden is often the frostiest. Waterlogged compost freezes more readily, too. The single most effective move is to shift containers to a sheltered, south- or west-facing wall. A house wall radiates stored heat overnight, keeping the immediate area a degree or two warmer. Group pots closely together, with the hardiest at the outside and the most tender in the centre. Raise them onto feet or bricks so they are not sitting in a puddle. If you have a porch, cold frame, or unheated garage with a window, that is even better for the tenderest herbs. For ferns kept in containers, the same sheltered wall works well, though they prefer shade and consistent moisture rather than a baking south wall.

Watering: Less Is More

Overwatering kills more container herbs in winter than cold does. Growth slows almost to a stop, so the roots use very little water. Damp compost around the roots freezes solid, and the expanding ice can shear fine roots. Check pots every week or two, but only water when the top few centimetres are dry. Use tepid, not icy, water and do it in the morning so any excess can drain before nightfall. Empty saucers and drip trays after rain; never let pots stand in water. If a cold snap is forecast, skip watering altogether for a few days. Tender herbs such as lemon verbena would rather be slightly dry than sodden.

Wrap Terracotta and Insulate Roots

Terracotta is porous: it absorbs water, and when that water freezes, the pot can crack. Even if it survives, the damp clay conducts cold straight to the rootball. Wrap the outside of terracotta pots with bubble wrap, hessian, or an old woollen blanket, secured with twine. A simpler method is to double-pot: stand the terracotta pot inside a slightly larger plastic or wooden container, filling the gap with straw, bark chippings, or crumpled newspaper. For added insulation, mulch the surface of the compost with a layer of horticultural fleece or dry leaves, but keep it away from the stems to avoid rot. If you have several pots, a simple cold frame made from straw bales and an old window works wonders. Ferns in terracotta benefit from the same wrapping, especially if they are in small pots.

Pruning, Airflow and Pest Checks

Don't cut tender herbs back hard in autumn. Those stems may look scruffy, but they shelter the crown and provide a little frost protection. Wait until spring, when you can see which growth has survived. Remove any dead, slimy leaves and fallen debris promptly, as these attract mould and slugs. Good airflow matters: crowded, stagnant air around wet foliage encourages botrytis. Space pots a little apart, or if they are grouped for warmth, check them weekly and remove any affected leaves. Winter can also bring aphids and whitefly on indoor herbs; inspect the undersides of leaves and wipe them off with a damp cloth. A quick check with a torch after dark will reveal slugs and snails hiding under pot rims.

A Cottage-Style Corner and Spring Recovery

If you have a sheltered corner by a wall, why not make a feature of your overwintering pots? A cottage-style grouping of terracotta pots, wrapped in hessian and nestled among evergreen ferns, hellebores and ivy, looks charming even in January. The ferns appreciate the same shelter and steady moisture, and their fronds hide the scruffier herbs. Come March, start to water a little more freely and move pots back into the light. Wait until all risk of frost has passed — usually late May in most of the UK — before putting tender herbs back outside permanently. Repot any that have outgrown their containers, using fresh, peat-free compost. With luck, your basil, tarragon and lemon verbena will reward you with a full season of scent and flavour.