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Most herbs sown too early grow long and pale, and most sown too late never catch up. A simple calendar avoids both: the slow ones start in late winter, the warmth lovers in spring, and the fast ones are sown again every few weeks.
This calendar is for a bright windowsill and a balcony in the UK and central Europe, where the last frost usually comes in late April or mid May. In a mild city flat you can move everything a week or two earlier.
Below: what to sow in each month, how warm each herb needs to be to germinate, and which herbs are better bought as plants.
Start chillies and parsley on the windowsill in February, basil, thyme, oregano and sage in March and April at 18 to 25 °C. Sow coriander and dill straight into their final pots from April and again every three to four weeks. Move tender herbs outside after mid May. Sow parsley and chervil again in August, and grow cress and microgreens indoors in winter.
Why does the sowing date matter?
Seedlings need light more than anything else. In January and early February a windowsill gets too little of it, so seedlings stretch towards the glass and fall over. From late February the days are long enough for most herbs.
Temperature is the second factor. Basil germinates poorly below 18 °C, while parsley and chives are happy at 15 °C. A cold windowsill above a closed radiator can be several degrees cooler than the room.
What should you sow in each month?
| Month | Sow indoors | Sow outdoors or on the balcony |
|---|---|---|
| January | Microgreens, cress | Nothing |
| February | Chillies, parsley, chives | Nothing |
| March | Basil, thyme, oregano, sage, lemon balm | Nothing, except cress under glass |
| April | Basil, coriander, dill (in final pots) | Parsley, chives, chervil in mild weather |
| May | Second sowing of basil | Basil, dill, coriander after mid May |
| June to July | Coriander, dill, chervil every 3 to 4 weeks | Same, in part shade |
| August | Parsley, chervil for autumn | Parsley, rocket |
| September | Chives, cress | Rocket, cress |
| October to December | Microgreens, cress | Nothing |
When should you sow basil?
Basil is the herb most often sown too early. Sow it from mid March on a warm windowsill, at least 20 °C, and press the seeds lightly into the compost without covering them deeply. It germinates in five to ten days.
Seedlings sown in March are ready to go outside after mid May, when nights stay above 10 °C. A second sowing in May gives fresh plants for late summer. Our guide to growing basil indoors explains pinching and harvesting.
Which herbs germinate slowly?
Parsley is famously slow: two to four weeks. Soaking the seeds in lukewarm water overnight helps. Sow it in February or March indoors, or from April outside, and do not give up after a fortnight.
Chives take ten to fourteen days, and thyme, oregano and sage ten to twenty. Thyme and oregano seeds are tiny and need light to germinate, so scatter them on the surface and only press them in.
How warm do herb seeds need to be?
| Herb | Germination temperature | Days to germinate | Cover seeds? |
|---|---|---|---|
| Basil | 20 to 25 °C | 5 to 10 | Barely |
| Parsley | 15 to 20 °C | 14 to 28 | About 1 cm |
| Chives | 15 to 20 °C | 10 to 14 | About 1 cm |
| Thyme | 18 to 22 °C | 10 to 20 | No, light germinator |
| Oregano | 18 to 22 °C | 7 to 14 | No, light germinator |
| Coriander | 15 to 20 °C | 7 to 14 | About 1 cm |
| Dill | 15 to 20 °C | 7 to 14 | Thinly |
| Sage | 18 to 22 °C | 10 to 20 | Thinly |
Which herbs should be sown straight into their final pot?
Coriander and dill grow a long taproot and dislike being transplanted. Sow them where they will grow, in a pot at least 20 cm deep, and thin the seedlings to a few centimetres apart.
Both bolt quickly in summer heat, which is why small sowings every three to four weeks give a steady supply rather than one big crop that flowers in June.
Which herbs are better bought as plants?
- Rosemary and lavender grow very slowly from seed; a young plant gives a harvest the same year.
- Mint varieties such as peppermint do not come true from seed; buy a plant or take a cutting.
- French tarragon is grown from cuttings; tarragon seed is usually the less aromatic Russian type.
Where will the seedlings grow on?
Once seedlings have two or three pairs of true leaves, they need more space and light. Prick them out into individual pots and harden them off for a week before moving them outside: a few hours outdoors on the first day, then longer each day.
On a small balcony, height helps. The Urban Planty Vertical Garden holds nine pots on a telescopic pole clamped between floor and ceiling, on less than one square metre, and each pot has a 300 ml water reservoir. It costs €149 with free shipping and needs no drilling. More about the vertical garden without drilling, and about avoiding common mistakes in our balcony herb garden guide.
In the darkest months, windowsill herbs grow slowly. Cress and microgreens are the exception and give a harvest within two weeks even in December.
Frequently asked questions
When should I start sowing herbs indoors?
Start sowing herbs indoors in February with chillies, parsley and chives, then basil, thyme, oregano and sage from mid March, when light is sufficient on a bright windowsill.
When can I sow basil outside?
Basil can be sown or planted outside after mid May, when nights stay above 10 °C. Indoors on a warm windowsill it can be sown from mid March.
Why is my parsley not germinating?
Parsley often takes two to four weeks to germinate. Soaking the seeds overnight and keeping the compost evenly moist at 15 to 20 °C speeds it up.
How often should I sow coriander?
Sow coriander every three to four weeks from April to August, straight into its final pot. Coriander runs to flower quickly in summer heat, so frequent small sowings give a steady supply.
