A windowsill garden: what can you actually grow indoors?

How much light does your window give?

A south-facing window gives six to eight hours of direct light in summer: enough for almost everything in this guide, including heat-loving herbs. East and west deliver three to five hours — fine for lettuce, spinach, radish and mint, too little for tomatoes or peppers.

A north-facing window gives bright light but never direct sun. Only leafy crops and mint grow there, and even those slowly. To do more, a grow light is not a luxury but a requirement.

Look at what stands outside, too. A tree, a shed or the neighbours' balcony above you can halve your hours, and you only notice when nothing happens.

Pots, compost and the glass trap

Fifteen centimetres of depth is the minimum, twenty is more comfortable. More important than the size are the holes in the base: a decorative pot without drainage is the most common cause of death on a windowsill.

Do not push pots against the glass. In winter it is nearly outdoor temperature there at night; in summer it hits thirty degrees behind glass. A few centimetres of clearance solves both.

Use ordinary potting compost, not garden soil. Garden soil compacts in a pot, holds too much water and brings weed seed indoors.

Watering indoors

Less evaporates indoors than outside, so you water less than you expect. Feel two centimetres down with a finger: if it is moist there, wait another day.

During the heating season that flips. A radiator under the windowsill dries the air and the root ball faster than summer sun. Check every other day rather than twice a week.

The winter dip

Between November and February there is simply too little daylight in northern Europe. Plants do not die, they stall: long floppy stems, small leaves, little flavour.

You have two options. Pause and sow again in March, or hang a grow light and give twelve to fourteen hours a day. Muddling through without either mostly produces disappointment.