Start with the light, not the pot

Most windowsill herbs fail for one reason: not enough light. A kitchen window facing south or south-west, with four to six hours of direct sun in summer, will carry basil, parsley, chives and mint happily. An east-facing sill suits parsley and mint but leaves basil sulking and leggy. A north-facing window is fine for mint and little else, and even then it will stretch towards the glass.

Two things are worth knowing about the sill itself. Windows trap heat and cold: on a sunny July afternoon the air behind the glass can reach 35°C, and on a January night it can drop close to freezing. Basil dislikes anything below about 10°C and will blacken at the leaf edges. Turn every pot a quarter turn each time you water, too, otherwise plants lean permanently towards the pane and grow lopsided.

Containers, compost and drainage

Herbs need root room and free drainage, which usually means a pot one size larger than the one they arrived in. A supermarket basil in a 9cm pot wants moving into something 15–18cm across within a week; leaving it crowded is the quickest way to lose it.

• Pots: terracotta breathes and dries out faster, which suits chives and parsley. Glazed or plastic pots hold moisture longer, better for basil and mint. All need drainage holes.
• Saucers: essential on a painted sill, but empty them twenty minutes after watering. Standing water rots roots faster than almost anything else.
• Compost: a peat-free multipurpose mixed with a handful of horticultural grit per pot gives the open texture herbs want. John Innes No. 1 is a good alternative for parsley and chives.
• Size: a 15cm pot takes one basil or one parsley plant. Mint is a spreader, so give it a pot of its own or it will colonise its neighbours.

Parsley, basil, mint and chives: what each one wants

• Basil – the thirstiest for sun and warmth. Keep it in the sunniest spot, water little and often, and never let it sit in a cold draught. Pinch out the growing tips regularly to stop it flowering.
• Parsley – tolerant of partial shade and cooler sills. Flat-leaf types have better flavour than curly. It is a biennial, so a plant sown this year will run to seed next spring; sow a fresh pot each autumn to keep a supply going.
• Mint – the most forgiving of the four, and the most invasive. Spearmint is the best for cooking. It will tolerate a north sill, but keep it in its own pot and cut it back hard if it flops.
• Chives – happy in a bright spot out of fierce midday sun. Snip the leaves rather than pulling them, and the clump will keep producing for years. The purple flowers are edible and worth leaving on one or two stems.

Watering: the habit that makes or breaks windowsill herbs

Indoor pots dry out from the top down and from the sides inwards, so a finger pushed 2cm into the compost tells you more than the surface does. If it feels dry at that depth, water; if it feels cool and damp, wait a day.

Water in the morning where you can, letting the pot drain properly before it goes back on the saucer. Little and often suits basil; a thorough soak followed by a slight drying-out suits parsley, chives and mint better. In winter, cut watering right back — most windowsill herbs are semi-dormant and would rather be dry than wet. Yellowing lower leaves are usually a sign of overwatering, not thirst.

Feeding and pinching back

Compost holds enough nutrients for about six weeks. After that, feed established plants every fortnight through spring and summer with a weak liquid feed — half the strength recommended on the bottle is plenty. Basil and chives benefit most; parsley and mint need very little.

Harvesting is really pruning. Take basil tips from just above a pair of leaves and the plant will fork into two stems. Snip chives about 2cm above the compost. Cut parsley stems from the outside of the clump, not the middle. With mint, cut whole stems rather than picking leaves. Never strip more than a third of a plant at once, and give it a week to recover before cutting again.

Common problems and easy fixes

• Long, pale, spindly growth: not enough light. Move the pot closer to the glass or add a small clip-on lamp.
• Yellow lower leaves: usually soggy compost. Let the pot dry out, then water less often and empty the saucer.
• Tiny black flies around the compost: fungus gnats, drawn to constantly wet surfaces. Water from below for a fortnight and top the compost with a thin layer of grit.
• Greenfly or whitefly: rinse leaves under a lukewarm tap, or wipe them with a damp cloth, and check new growth weekly.
• Basil collapsing overnight: almost always cold. Move it away from the glass on frosty nights.

Get these few things right and a kitchen sill will give you cut herbs from March until late autumn, with a decent winter supply of parsley, mint and chives to see you through.