How to grow herbs on a windowsill, and keep them from going leggy

Light is what makes or breaks a windowsill herb. Without enough, herbs grow "leggy and spindly" (Illinois Extension): long, weak stems with small, pale leaves and little flavour. Everything else in this guide (pot, water, feeding, cutting) matters less than getting the light right.

How to grow herbs on a windowsill

1. Choose your sunniest window.

   

   Our sources ask for different amounts of direct sun: at least 5 to 6 hours (NC State), at least 6 (Illinois), or about 8 (Iowa State, which says some herbs manage on 6). In the northern hemisphere a south-facing window gives the most; Iowa State says a bright east- or west-facing window can also work. In the southern hemisphere, use a north-facing window.

   You should see: sunlight falling directly on the windowsill for most of the day, not just a bright room.

2. Give each herb its own pot with a drainage hole.

   

   Iowa State Extension recommends growing each kind of herb in its own container. Herbs differ in how much water they like (see the table below), so separate pots let you water each one correctly.

   A supermarket pot of basil is usually crowded with seedlings. The RHS says to divide it and repot the clumps promptly.

   You should see: one herb per pot, firmed in at the same depth as before, with mix a little below the rim.

3. Keep them warm, but away from heaters.

   

   Illinois Extension suggests 60 to 70 °F (about 16 to 21 °C) and keeping herbs away from heating vents, which dry them out. Basil needs the most warmth: the RHS says it isn't hardy in the UK.

   You should see: herbs in the sun but not directly above a radiator or vent.

4. Water only when the mix is dry about 2.5 cm down.

   

   Most herbs don't like wet soil, so let the mix dry between waterings (Iowa State). NC State Extension says to water only when the mix is dry at least an inch (2.5 cm) down, then water until it drains from the hole and tip away the runoff. Rosemary is the exception: Illinois Extension says its mix should never dry out completely.

   Water basil in the morning if you can: the RHS says it dislikes wet roots overnight and doesn't like its leaves splashed.

   You should see: water running from the drainage hole, then an empty saucer. Our watering guide shows the checks in detail.

5. Add a grow light if the window is too dark.

   

   In winter, or at a shady window, a grow light fills the gap. Iowa State Extension says to place it 6 to 12 inches (15 to 30 cm) from the leaves and plug it into a timer set for 12 to 16 hours a day. Illinois Extension gives 12 to 14 hours for fluorescent lights at the same distance.

   You should see: short, sturdy new shoots with leaves close together, not long gaps of bare stem.

6. Feed lightly in spring and summer only.

   

   Iowa State Extension suggests an all-purpose fertiliser at half or a quarter of the normal strength, from early spring through summer, and none in winter. NC State gives a quarter to half the label rate for synthetic fertiliser. Don't overdo it: Illinois Extension says too much feed can reduce aroma and taste.

   You should see: steady green growth through spring and summer, and no feeding at all in winter (Iowa State).

7. Snip the tips often, and never take more than the plant can regrow.

   

   Pinching out the growing tip makes basil branch and grow bushier (RHS). For leafy annuals such as basil and parsley, cut just above a leaf or pair of leaves and leave about 4 to 6 inches (10 to 15 cm) of stem to regrow; for perennials such as chives, mint, oregano and thyme, take only the top third (Iowa State). Cut parsley and coriander stalks at the base (Illinois Extension).

   You should see: two new shoots growing from just below each cut within a couple of weeks.

Herb by herb

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