Pick Clean, Pick Dry

There is something quietly satisfying about filling a jar from the hedgerow in July and opening it in January, when the garden is grey and the kettle is on. The secret to herbs that keep their colour and their flavour through the winter begins long before you reach for the string, though. It begins with when and where you pick.

Harvest on a dry morning, once the dew has lifted but before the sun grows fierce. Mid-morning to early afternoon is ideal. Plants gathered wet can turn mouldy inside the bundle, and herbs cut in blazing heat have already begun to lose the aromatic oils that make them worth keeping. If rain is forecast, wait. A day or two makes no difference to the plant, but it makes a great deal of difference to your jar.

Where you pick matters just as much. Avoid roadside verges, where exhaust fumes and spray drift settle into the leaves, and steer clear of field edges you know are treated. Footpaths popular with dog walkers are best left alone, at least at the height a Labrador can reach. Choose instead a quiet corner of a meadow, an unsprayed garden hedge or a woodland ride. Take only what you need, and never strip a plant bare — nettles will regrow cheerfully if you take the top few leaves, but a patch grubbed up by the roots takes years to recover.

Herbs That Dry Beautifully

Some herbs dry far better than others. The reliable ones are those with plenty of aromatic oil and relatively little water in their leaves.

• Nettles — pick the top two or three pairs of leaves in late spring, before the plants flower and set seed. Wear gloves, and choose young, deep green growth rather than anything tough and leggy.
• Mint — cut stems just before the flowers open, when the scent is at its strongest. Spearmint and apple mint both dry well.
• Rosemary — can be gathered almost any month, though midsummer is best. Take woody stems rather than soft new tips, which shrivel to nothing.
• Also worth a bundle — lemon balm, thyme, sage, marjoram, fennel and lemon verbena.

Unless your herbs are genuinely gritty, don't wash them. If you must rinse, shake them well and lay them on a tea towel until they are bone dry before you do anything else. Pick out damaged leaves, grass seeds and the inevitable small passengers, and give the stems a shake outdoors.

Air-Drying in a Dark Room

The old-fashioned method still works best. Gather five to eight stems into a loose bunch and tie them with garden string, leaving a long tail so you can hang the bundle from a hook, a line or the rungs of an airing rack. Tie them loosely — you want air moving between the stems, not a compressed fistful that will sweat and rot in the middle.

Hang them upside down in a dark, dry, well-ventilated room. This is the part people get wrong. Light fades colour and breaks down the oils that carry flavour, so a bright windowsill is the worst place in the house. A spare bedroom with the curtain drawn, a cool pantry, a garage with the window blocked out — all are ideal. Kitchens and bathrooms are not: steam undoes weeks of work in an afternoon.

For nettles and other awkward, thick-stemmed plants, try a brown paper bag instead. Punch a dozen holes in the sides, pop the herbs in loosely, fold the top over and hang the bag up. The paper keeps off the light and lets the moisture out. Small leaves and seed heads dry well this way.

Depending on the weather and the plant, drying takes one to three weeks. Rosemary is slow; mint is quick. Test a stem by bending it: it should snap crisply rather than bend like leather. A leaf should crumble between your fingers.

Conditioning and Storing Your Jars

Before you commit a whole harvest to a jar, condition it. Fill a clean, dry jar loosely, leave the lid off for a few days and shake it daily. If you see any misting on the glass, the herbs are still holding moisture — tip them back out and dry them for another week. This small step is what separates herbs that keep for a year from herbs that turn to grey fluff by November.

Once they are properly dry, fill your jars, press the lids down firmly and label every single one with the herb and the month and year. Nettle and mint look remarkably similar by candlelight in January. Store the jars in a cool, dark cupboard away from the cooker, and keep them whole rather than crushed — crumble the leaves as you use them, and the flavour stays far longer.

Check your store once a month. Greyish fuzz, a musty smell or clumped leaves mean the batch has gone over; throw the whole jar out rather than picking out the obvious mould, as the spores will have spread through it. Herbs kept cool, dark and dry will hold their quality for about a year, so use the oldest jars first.

Using Your Store Through Winter

A heaped teaspoon of dried herb per mug is about right, or two to three teaspoons if you are using fresh. Pour on water that has just come off the boil, cover the mug with a saucer and leave it for five to ten minutes — the lid keeps the volatile oils in the cup rather than in the kitchen. Nettle tea is green, grassy and faintly minerally, and takes kindly to a pinch of dried mint. Rosemary is far more assertive: use it sparingly in tea, and generously in stuffings, roast lamb and winter soups.

A word of sense, finally. Herbs are food, not medicine, and a foraged tea is no substitute for a visit to the doctor. If you are pregnant, breastfeeding or taking prescription medication, have a word with your pharmacist or GP before making a habit of nettle or rosemary infusions. And if a jar smells musty, however much effort went into it, let it go. There is always another summer.