Why a Sunny Windowsill Suits Herbs So Well

A south-facing windowsill is one of the kindest places in a British home for growing herbs. It catches the most light, it stays warmer than the garden through spring and autumn, and it shelters plants from wind and driving rain. Most of the herbs we reach for in the kitchen — basil, mint and thyme especially — come from sunny, free-draining hillsides, so a bright sill with a pot of gritty compost mimics the conditions they evolved in.

Aim for at least six hours of direct sun a day. If your sill faces east, you can still grow mint and thyme comfortably; basil will be a little slower and leggier but perfectly usable. West and north-facing sills suit mint best, though even that will sulk in deep shade. Turn your pots a quarter-turn every few days so the plants grow straight rather than leaning into the glass.

Choosing Pots and Getting Drainage Right

Almost all windowsill herb failures come down to water sitting around the roots. Herbs hate soggy feet far more than they hate drying out, so drainage is the first thing to sort.

• Size: a 15–20cm pot suits basil and most thymes. Mint spreads aggressively and wants a 25cm pot, or better still its own pot kept well away from the others.
• Material: terracotta breathes and dries out faster, which suits thyme. Glazed ceramic or plastic holds moisture longer, which basil prefers. Both are fine as long as there are holes in the base.
• Compost: use a peat-free multipurpose compost mixed with grit or perlite at roughly three parts compost to one part grit. For thyme, go grittier still — half and half is not too much.
• Saucers: keep them, but empty them. A pot standing in an inch of water for a day is enough to start root rot.

Skip garden soil entirely. It compacts in a pot, drains poorly and often brings in weeds and grubs. Fresh compost also gives young plants the nutrients they need for the first few weeks.

Three Dependable Herbs to Start With

Basil, mint and thyme cover most everyday cooking and each behaves differently, so a little knowledge goes a long way.

• Basil is the thirstiest and the fussiest about cold. Sow seeds indoors from March, or buy a supermarket pot and split it into two or three smaller pots straight away — the crowded seedlings in those pots strangle each other within a fortnight. Keep it warm, water little and often, and pinch out the growing tips regularly.
• Mint is almost indestructible and will happily grow on a shadier sill. Buy a small plant rather than sowing seed, and keep it in its own pot; its roots travel and it will invade anything nearby. Spearmint is gentler for cooking, peppermint sharper for tea.
• Thyme is the toughest of the three. It tolerates neglect, drought and cool nights, and it comes back year after year if you keep it lean and gritty. Water it sparingly — once the compost is dry an inch down — and never let it sit wet.

Watering and Feeding Through the Year

In summer, check your pots every morning. A small pot on a hot sill can dry out in a single day, and basil in particular will wilt dramatically by mid-afternoon. Water from the top until a little runs out of the base, then tip the saucer. In winter, cut right back: thyme and mint may need water only every week or two, and basil usually gives up altogether once light levels drop.

Feed fortnightly from April to September with a general-purpose liquid feed at half strength. Basil and mint appreciate it most; thyme needs very little and can be left un-fed if it was potted in fresh compost that year. Overfeeding produces soft, floppy growth with weak flavour and invites pests.

Harvesting So the Plants Keep Producing

Regular picking is what keeps a windowsill herb productive. Treat it as pruning rather than stealing.

• Pinch basil just above a pair of leaves, taking the growing tip with it. Two new shoots will break from that point. Never take more than a third of the plant at once.
• Cut mint stems back to a leaf joint, and remove any flower buds as soon as they appear — flowering signals the leaves to toughen and lose flavour.
• Snip thyme sprigs with scissors rather than pulling at them, which disturbs the roots. Light, frequent cutting keeps it bushy.

Use the leaves straight away where you can. Soft herbs like basil and mint lose their scent quickly once picked, so add them at the end of cooking rather than the beginning.

Sorting Out Common Problems

If a plant is pale and stretchy with wide gaps between the leaves, it wants more light. Move it to a brighter spot and pinch out the leggy stems. Yellow lower leaves usually mean overwatering; let the compost dry out properly before the next drink and check the saucer is empty. Compost that smells sour or is covered in green algae on the surface needs replacing.

Small greenflies cluster on soft new basil growth. Wipe them off with your fingers or a damp cloth, and check the undersides of leaves every few days. Whitefly rise in a cloud when you touch the plant — a yellow sticky trap on the sill helps keep numbers down. Mint sometimes develops orange-brown spots of rust; pick off affected leaves promptly, water at the base rather than over the leaves, and give the plant more air.

Finally, a windowsill is a small space, so resist overcrowding. Two or three pots with room around them will out-perform six crammed together, and you will actually be able to reach the leaves when you need them.