A balcony vegetable garden in Belgium, month by month
Pot size, watering and sowing dates, from January to December, for your vegetables in pots on a Belgian balcony.
A balcony vegetable garden is not a small garden. It is soil in containers. It dries out and freezes faster than soil in the ground. A 20-litre bag soaked with water weighs 15 to 20 kg on the balcony floor. Gardening calendars assume deep soil, which holds water and heat. This guide takes the three constraints of a balcony one by one. It then runs through the Belgian year month by month.
The three constraints of a balcony
The sun
All vegetables need sun, but not as much. Brussels Environment (Bruxelles Environnement) distinguishes three cases. More than 6 hours a day is full sun. From 3 to 6 hours, partial shade. Less than 3 hours, shade. On a fine day, watch your balcony at 9 am, 1 pm and 5 pm. Count the hours of sun.
Tomatoes, cucumbers and beans want full sun. Chard, radishes, curly endive and nasturtium accept partial shade. Mint prefers it.
The volume of soil
The container is your whole garden. A pot holds less heat than the ground. A young shoot freezes faster there. Volume decides water, food and protection from the cold.
Wind and weight
On a high or exposed balcony, put up a permeable windbreak and tie down fragile plants. Count the weight too. A 20-litre bag of potting mix weighs 6 to 8 kg dry and 15 to 20 kg soaked with water. Check the load your balcony can carry. Keep containers against the wall. Use saucers so you do not water the neighbour below. Weigh down pots that the wind could knock over.
What volume for which crop?
Brussels Environment sorts crops into three container sizes. For most vegetables, 20 to 30 cm of depth is enough, even in a window box.
| Container | Suitable crops |
|---|---|
| 0.5 to 5 litres (15 to 20 cm across) | Radish, beetroot, short carrot, garlic, onion, lettuces, spinach, basil, chives, parsley, mint, nasturtium, mangetout pea, broad bean |
| 10 to 25 litres (20 to 30 cm across) | Leek, chard, celery, thyme, rosemary, cauliflower, cucumber, climbing bean, pepper, chilli, strawberry plant |
| 30 litres and more (30 to 40 cm across) | Tomato, aubergine, courgette, potato, cabbage |
Leaflets differ for the big plants. Another Brussels leaflet accepts 10 litres for a courgette. ProSpecieRara advises 20 litres of soil for a tomato. An American guide says at least 5 gallons, about 19 litres. Dwarf varieties need less. The sheet for our Balconi jaune cherry tomato states 5 to 7 litres. For a normal-size tomato or courgette, aim for 20 litres at least, 30 if your balcony allows it.
Varieties that hold up in pots
Look for low plants, with a short cycle, or ones you pick leaf by leaf. The catalogue offers several for your pot vegetables.
- Balconi jaune cherry tomato. A compact bush, which the RHS recommends for pots and window sills. Our sheet states 30 to 50 cm tall, with no pruning and no side shoots to remove.
- Cut-and-come-again lettuces (Red Star Bowl, Oreille du diable or the mix). You cut the leaves as you go. The plant starts again.
- Chandelle de feu radish. According to Brussels Environment, a radish takes 18 to 50 days from seed to harvest, depending on the season. Its root is about 15 cm long. Allow at least 20 cm of depth.
- La Victoire dwarf mangetout bean. Brussels Environment advises a dwarf variety when space is tight. Sow after the last frosty nights, in warmed soil.
- Carotte hâtive d'Amsterdam. The Meuse-Rhine-Moselle network (Réseau Meuse-Rhin-Moselle) classes it among the early half-long carrots, with roots of 12 to 20 cm. Allow at least 25 cm of depth, so a container from the medium class.
- Grand vert basil, curly parsley, common thyme. Basil and parsley are happy in a small container. Thyme needs 10 to 25 litres.
- Dwarf nasturtium in mixed colours. Its flowers are edible. According to Brussels Environment, it also serves as an aphid trap plant.
Potting mix, holes and watering
The potting mix
Brussels Environment suggests two thirds soil or potting mix to one third compost. Choose a peat-free mix that can be used in organic growing, based on coconut fibre or green waste. ProSpecieRara also advises it for tomatoes in pots. Each spring, replace a fifth of the mix with ripe compost. Also change vegetable from the year before.
The holes
A container with no holes drowns the roots. Drill the bottom if needed. Then cover the holes with pot shards, cork stoppers, cardboard or a piece of geotextile. The water goes through and the mix stays. Leave 3 to 5 cm between the mix and the rim, for watering and for mulching.
Watering
Watering decides the season. A container dries faster than the ground. A terracotta or stone pot dries faster than a plastic one. Push a finger into the mix. It should be moist deep down. Water once to several times a week, more often when it is hot. Water at the end of the day, with rainwater if you have some. Cover the mix with dead leaves, dried grass clippings or straw to limit evaporation. A container with a water reserve gives you autonomy in summer. Stagnant water can still make the roots rot.
Fruiting plants (tomato, courgette, cucumber) have big needs. Add a diluted organic fertiliser (1 to 10) every week or every 10 days.
The calendar, month by month
Temperatures are the RMI 1991-2020 normals at Uccle. The dates hold for the centre of the country. In the east and at altitude, May frosts are more frequent. On 12 May 2020, it froze down to minus 3.6 °C at Elsenborn and minus 3.2 °C at Saint-Hubert, according to the RMI quoted by the RTBF. The Ice Saints (11, 12 and 13 May) serve as a landmark.
| Month | At Uccle | What to do on your balcony |
|---|---|---|
| January | 3.7 °C | Nothing goes out yet. Count your balcony's hours of sun, clean second-hand pots and sort your seeds. |
| February | 4.2 °C | Sow chillies and aubergines in the warm, under a lamp. Outside, you can already sow broad beans in pots, until April. |
| March | 7.1 °C | Sow tomatoes in the warm, between 20 and 25 °C. Early March under a lamp, mid-March on a windowsill. Outside, sow radishes, spinach and smooth-seeded peas. Plant strawberry plants. |
| April | 10.4 °C | Sow radishes, cut-and-come-again lettuces and spinach outside. When the temperature goes above 5 °C, put plants raised in the warm out for a few hours in the shade. Bring them in in the evening. |
| May | 13.9 °C | Harden the plants off for seven to ten days. After the Ice Saints, if the forecast allows, tomatoes, courgettes, peppers, aubergines and basil go out for good. Plant cucumbers, sow dwarf beans. |
| June | 16.7 °C | Stake the tomatoes and pinch out the side shoots, except on bush varieties. Keep an eye on watering and feed your fruiting plants. |
| July | 18.7 °C | Last sowings of beans early in the month, of curly endive before the end of the month. Mulch thickly. Put salads in the shade in the afternoon. |
| August | 18.4 °C | Sow radishes and spinach for autumn. Plant the strawberry plants. |
| September | 15.2 °C | Last sowings of radishes (until mid-September) and of spinach (until the end of the month). Strawberry plants to plant until the end of the month. |
| October | 11.3 °C | Sow hardy broad beans, until early November. Plant garlic. Bring in plants that fear frost. |
| November | 7.2 °C | Empty the summer pots and cover the mix with cardboard or dead leaves. Plant garlic until mid-November. |
| December | 4.3 °C | Store the terracotta pots out of the frost. |
The app gives the sowing date of each of your packets for your address.
Before mid-May, tomatoes, courgettes, peppers, aubergines, beans and basil stay under cover. After the Ice Saints, put them out when all the minimums forecast for your town over seven days are above 5 °C. Our guide to the Ice Saints explains this rule. If they are already outside, bring them in when the forecast announces frost, or even just 1 to 2 °C (Good Food Brussels). The forecast gives the temperature at 1.50 m above the ground. At ground level, it is colder.
Overwintering your pots
To let die. Tomatoes, courgettes, cucumbers, beans and basil do not get through winter. At the end of autumn, remove the plants and cover the mix with cardboard or dead leaves.
To bring in. A frost-tender plant you want to keep, like a chilli plant, comes in near a window before the first cold nights.
To protect. Terracotta pots fear frost. Store them under cover. Broad beans sown in October get through winter as small plants. They recover from a moderate frost. Protect them from a hard frost or a frost that lasts all day (Good Food Brussels). Cut the mint back to 10 cm before winter.
No date shift holds for every balcony. In town, buildings and roads warm the air a little. You can start earlier in spring and finish later in autumn. To find your own gap, put a min-max thermometer at plant height. Compare its readings with the nearest weather station.
Further reading
- The collection: Balcony & pots
- The Start page: Tell us which seeds you have, and we tell you when to sow each one where you live
- Three other guides: Sowing calendar for Belgium, The Ice Saints in Belgium and Growing degree days
Photo: Tom Jur, Unsplash
Sources
- Bruxelles Environnement, Mijn balkon moestuin (adviesblad Telen in de stad, septembre 2018) : soleil, poids, contenants, substrat, tailles de contenant par culture, arrosage, dates de semis, hivernage
- Bruxelles Environnement, Infofiches moestuin 11 : Potten voor bloemen en groenten (29 mai 2012) : trous de drainage, profondeur, courgette
- Good Food Brussels, article Bang voor die enge boze temperaturen onder nul ? (PDF daté de janvier 2025) : gel jusqu'à la mi-mai, pots et inertie thermique, endurcissement, plantes à protéger
- Bruxelles Environnement, Évolution du climat en Région bruxelloise, température et précipitations (fiche documentée, janvier 2021) : normales IRM 1991-2020 pour Uccle
- RTBF, Mamert, Pancrace et Servais : pourquoi sont-ils des saints de glace ? (gelée du 12 mai 2020, citant l'IRM)
- ProSpecieRara (Suisse), Tomates urbaines, guide étape par étape : Tomates (semis dès la mi-mars, endurcissement, plantation après les Saints de Glace, 20 litres de terre)
- Royal Horticultural Society, Solanum lycopersicum 'Balconi Yellow' (port buissonnant, 0,1 à 0,5 m, pour pots)
- Réseau Meuse-Rhin-Moselle (Nature & Progrès Belgique), Fiche technique Carotte, soins de culture (janvier 2018) : groupes de carottes, demi-longues hâtives de 12 à 20 cm
- The Old Farmer's Almanac, Container gardening vegetables (5 gallons au minimum pour une tomate)
- Velt, Wat kun je in de zomer en het najaar zaaien en planten ? (dates les plus tardives pour un automne normal : chicorée frisée, ail)
- Cycle en Terre, Calendrier des semis 2022 (conditions de culture en Belgique, diffusé par Nature & Progrès Belgique)
- Vegiwise, fiches Tomate cerise Balconi jaune, Radis Chandelle de Feu, Carotte hâtive d'Amsterdam, Haricot nain mangetout La Victoire (consultées le 17/10/2026)
He gardens in Belgium and tries out in his own vegetable patch what the app recommends. His articles always start from a source you can check and a step you can take this weekend.
