A small windowsill, a genuine saving

Fresh herbs are one of the easiest sustainability wins available in a British kitchen. A bunch of basil or coriander bought from the supermarket has usually been grown under glass somewhere warmer, packed in a plastic sleeve, chilled in transit and driven or flown hundreds of miles before it reaches the shelf. It then sits in the fridge door, wilts quietly, and half of it ends up in the food waste caddy. Growing your own on the windowsill replaces that whole chain with a pot, some compost and a few minutes of attention each week.

The plants themselves are undemanding, but they are not indestructible. Most windowsill failures come down to three things: not enough light, too much water, and pots that are too small. Get those right and a kitchen window can supply you with herbs from March through to November, and a good deal longer if you choose the spot carefully.

Light is the first thing to check

Herbs are sun-lovers. A south-facing windowsill that gets six hours or more of direct light is ideal. East and west facing sills will work for parsley, mint and chives, but basil and rosemary will stretch, pale and sulk. A north-facing sill is genuinely difficult, and it is kinder to choose a different project than to fight it.

A few practical details make a real difference:

• Move pots a few centimetres back from the glass in high summer, where leaves can scorch, and forward in winter when light is scarce.
• Turn each pot a quarter turn every week so stems grow straight rather than leaning towards the pane.
• Keep pots away from directly above a radiator — dry, rising heat stresses leaves and dries compost out fast.
• Clean the glass. Grime and condensation cut light more than most people expect.

Choose herbs that suit a windowsill

Basil, mint and parsley are the three most reliable choices, and each needs slightly different treatment.

• Basil is the classic. Buy a supermarket pot and split it: that dense clump is dozens of seedlings crammed together, which is why it collapses within a fortnight. Tease them apart, pot them into threes or fours in a 15cm pot of peat-free multipurpose compost, and water from below.
• Mint is almost indestructible, but it spreads by underground runners and will swamp anything sharing its pot. Give it a container of its own, keep it watered, and cut it often. Spearmint is milder; Moroccan mint makes excellent tea.
• Parsley is slower and needs patience — seed can take three weeks or more to germinate. Flat-leaf has better flavour than curly, and a shop-bought plant divided into two pots is a quicker start.

If you have a bright sill and want to experiment, add chives, thyme, oregano or a compact rosemary. Coriander bolts quickly in warmth, so it is best sown little and often rather than kept going indefinitely.

Pots, compost and drainage

Use containers with holes in the base, and always a saucer or a small tray. Terracotta dries out faster; plastic holds moisture longer. Either is fine, but avoid decorative pots with no drainage — roots sitting in soggy compost rot within days.

Fill with a peat-free multipurpose compost, leaving a centimetre below the rim for watering. A layer of grit on the surface keeps compost off the leaves and reduces the fungus gnats that thrive in damp, undisturbed pots. Group pots together if you can: they shade each other slightly and create a little humid microclimate that suits basil particularly well.

Watering, feeding and the daily glance

Overwatering kills more windowsill herbs than drought. Check the compost with a finger before you reach for the jug: if it is damp a centimetre down, wait. In summer a small pot may need water daily; in winter, once a week or less. Water in the morning where possible, and empty any saucer that is still full after half an hour.

Tap water is fine for most herbs, though basil and parsley prefer it at room temperature. From April to September, feed with a diluted liquid seaweed or tomato feed every fortnight — a weak solution is plenty. Winter is a rest period: cut back the watering, stop feeding, and expect growth to slow right down.

Harvesting so the plants keep producing

The golden rule is to cut little and often, because regular harvesting is what keeps herbs bushy rather than leggy.

• Pinch out basil above a pair of leaves, always taking a growing tip. Two new shoots will grow from that point.
• Never strip more than a third of a plant's leaves at once.
• Cut mint from the top, and remove flower buds to keep the leaves tender.
• Snip parsley from the outside stems first, working inwards as the plant matures.
• Use herbs straight away — a handful torn over a salad, stirred through pasta, or steeped in hot water for tea.

Yellowing lower leaves usually mean too much water; pale, spindly growth means too little light. Deal with the cause rather than simply feeding more. As autumn light fades, take cuttings or sow a fresh pot so you have young plants ready to take over when the older ones tire.