Herbs that live
by the glass.

Herbs are sun plants. Most culinary kinds — basil, rosemary, thyme, sage — want six or more hours of direct sun, and a windowsill delivers far less than the same spot outdoors: the glass, the frame and the depth of the reveal all cut the light, and intensity falls off quickly with every centimetre from the pane. In the northern hemisphere a south-facing window is the only one that reliably gives full sun; west gives a warm afternoon, east a gentler morning, and north gives bright shade that only mint, parsley and chives will tolerate. Swap south and north if you live south of the equator.

Do a simple test on a clear day: note the hour direct sun first lands on the sill and the hour it leaves. That number, not the compass point, is what the plant experiences. Keep pots within 15 cm of the glass, turn them a quarter each week so they do not lean, and wipe the pane — grime dims light noticeably.

From late autumn to late winter, day length and sun angle drop enough that even a south sill can fall short. A small full-spectrum LED 15–30 cm above the foliage for 12–14 hours a day fills the gap. Signs you need one: pale new growth, long gaps between leaves, and stems bending hard toward the window.

More windowsill herbs die of kindness than of neglect. Roots need air as well as water, and a pot that never dries suffocates them. Use a free-draining mix — a general peat-free compost with a third perlite or coarse grit — and a pot with a drainage hole standing in a saucer you empty after fifteen minutes.

Check before you water. Push a finger 2 cm into the soil: if it is dry there, water thoroughly until it runs from the hole, then leave the pot alone. The Mediterranean group — rosemary, thyme, sage — prefer to dry almost fully between waterings; the soft-leaved group — basil, mint, parsley, chives — like to stay lightly moist but never soggy.

Intervals shift with the season. A basil in a hot south window in July may need water every day or two; the same plant in January may go a week. Yellowing lower leaves plus wet soil means too much; crisp brown edges and a pot that feels light means too little. Repot when roots circle the base or water runs straight through, going up one pot size only. Feed sparingly — a half-strength liquid feed every few weeks in spring and summer, none at all in winter.

Most herbs multiply readily, which is the cheapest way to keep a rotation going as older plants tire.

Soft cuttings in water (basil, mint). Cut a 10 cm shoot just below a leaf node, strip the lower leaves, and stand it in a jar on a bright sill out of direct sun. Change the water every few days. Roots show in one to two weeks; pot up once they are 3–5 cm long and keep the compost moist for the first fortnight while water roots adapt to soil.

Semi-ripe cuttings (rosemary, thyme, sage). Take 8 cm tips in late spring or late summer from stems firm at the base but still green above. Strip the lower half, push into gritty compost, and cover loosely with a clear bag for humidity. These are slow — allow four to eight weeks — and dislike disturbance, so test for roots with a gentle tug rather than lifting them.

Division (chives, mint). Knock the plant out in spring, tease or cut the clump into fist-sized pieces with roots attached, and pot each separately.

From seed (parsley, coriander, dill). Taproots resent transplanting, so sow direct into the final, deep pot. Parsley germinates slowly — two to three weeks; soaking the seed overnight helps. Sow coriander little and often, because it bolts as soon as the weather warms.