Sowing calendar for Belgium: the month-by-month table

A calendar written for another climate can make you sow too early. Your tomato seedlings stretch for lack of light. A courgette put out too soon takes the last cold night. In soil that is still waterlogged, peas rot.

This one is set to Belgium. The frosts and temperatures come from the RMI records. The sowing dates follow the calendar of Cycle en Terre, a Belgian organic seed company. You can print it and pin it up in the garden shed.

Landmarks of the Belgian climate

At Uccle, according to the RMI (1991-2020 averages), the last frost day falls on average on 27 March and the first on 21 November. It freezes on average 5 days in March, 1 day in April and almost never in May. These are averages. Some years, it still freezes after the average date. For plants that like warmth, the RMI gives another landmark. It is the growing season, during which the mean temperature of the day reaches or passes 10 °C.

Liège and Uccle differ by only a few days. The calendar below holds for both. The Ardennes plateaus are almost a month behind.

The Ice Saints (Mamert, Pancrace and Servais, on 11, 12 and 13 May) therefore fall at the moment when the warm season sets in on the plain. The saying keeps the memory of frosts that damaged young plantings after 10 May. On 12 May 2020, it froze down to minus 3.6 °C at Elsenborn and minus 3.2 °C at Saint-Hubert. In the Ardennes, tradition even adds a fourth saint, Boniface, on 14 May.

How to read the table

"Under cover" means in a greenhouse, under a cold frame, on a windowsill or on a shelf under a lamp. "In the ground" means in the bed, or in an outdoor nursery bed for cabbages. The "Planting" column groups the young plants, sets and tubers put in place, for the crops where the planting-out date matters most. The dates hold for an average year in a plain garden like Liège or Brussels. "Early" and "late" specify the month when the window is short. The dates are summarised by species and vary from one variety to the next. A winter lettuce is not sown like a summer lettuce. The date on the packet wins over the one in the table.

Two moves matter as much as the date. Before sowing outside, squeeze a handful of soil. If it sticks in a ball, wait. If it crumbles, you can sow. Under cover, seedlings stretch when light is lacking. In February, a lamp on a timer, 14 to 16 hours a day, fixes the problem. Each seed also has its own germination temperature, from 20 to 30 °C for aubergine and from 10 to 15 °C for spinach.

The month-by-month table

For a specific crop, look for its name in the columns. The months where it appears give its windows. Some crops have two. Spinach is sown from January to April, then from late July to September. A vegetable that appears under "Under cover" and then under "Planting" has two dates to keep. You sow it, then you move it into the garden a few weeks later.

Five dates to set the year

• 15 March. A gardener's landmark. Crops that take months to grow (chilli, pepper, aubergine, celeriac, leek) are sown before it, because the Belgian summer is short.
• About 27 March. Last frost day on average at Uccle, 30 March at Liège. Sowings in the ground multiply. Carrot, radish and kohlrabi join the peas, broad beans and spinach. It can still freeze in April, one day on average at Uccle.
• 11 to 13 May. Ice Saints. Frost-tender plants go out from then on, if the forecast allows.
• 30 September. Last sowings in the ground for most leaf vegetables, turnips and lamb's lettuce. Winter spinach and hardy broad beans can still be sown in October.
• 7 October. End of the 10 °C period at Uccle (11 October at Liège). The vegetable garden slows down. Garlic and autumn shallots are planted from October to mid-December.

How much to shift in a greenhouse, on a balcony or in the Ardennes

The table holds for the plain. Elsewhere, first shift the sowing in the ground and the planting. Then count back for the sowing under cover.

An unheated greenhouse lets you sow and plant earlier. It does not remove the frost for all that. Keep a fleece within reach. We found no Belgian figure for the head start of a greenhouse or a south-facing balcony. Leave a min-max thermometer at plant height for two weeks. It gives you the gap at your place. The Ardennes, for its part, makes you wait. At Saint-Hubert, the last frost falls on average on 28 April, against 27 March at Uccle. The 10 °C period starts there on 11 June, against 14 May. Count on early June to put out frost-tender plants. Delay your sowings under cover by the same amount, so the young plants do not age in their pots.

For another town, the RMI publishes these statistics town by town, in its "Statistiques climatiques des communes belges" (climate statistics of Belgian municipalities) on meteo.be. Look up the average last frost and the 10 °C period for yours. Compare with Uccle or Liège, then shift the table by the gap.

Six common calendar mistakes

1. Sowing too early under cover. A tomato goes out into the garden around mid-May and spends about two months in its pot. Sown in February, it lacks light and stretches. Sow it in early March with a lamp, mid-March on a windowsill.
2. Putting out frost-tender plants too early. The forecast measures the temperature at 1.50 metres. At ground level, on a clear and windless night, it can be two or three degrees colder. Plant when the minimums forecast for your town stay above 5 °C for the coming seven days. Otherwise, wait, or keep a fleece within reach.
3. Sowing in cold, waterlogged soil. A pea swells with water before it germinates. In cold, waterlogged soil, it rots. The handful-of-soil test settles it.
4. Going from the windowsill to the garden in a single day. In the first sun, the leaves of an indoor plant burn. Count seven to ten days. For the first two days, put the plants out for two hours in the shade. Then move to half a day with the morning sun, then the whole day from the sixth day. Tomatoes, courgettes and basil finally sleep outside when the night no longer drops below 10 °C.
5. Sowing everything on the same day. A row of lettuces ripens all at once. Sow a small batch every two or three weeks, as long as the window stays open.
6. Putting the calendar away in July. Carrot is sown until July, lamb's lettuce from late August to September and spinach from late July to September.

Print the page or get the dates for your address

You can print this page from your browser. The Vegiwise app calculates the sowing date of each of your seeds for your climate, instead of a Belgian average.

Further reading

• The collection: To sow now
• The Start page: Tell us which seeds you have, and we tell you when to sow each one where you live
• Three other guides: The Ice Saints in Belgium, A vegetable garden on a balcony in Belgium and What to sow in September in Belgium

Photo: Elly M, Unsplash