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Tomatoes are the most popular crop on British balconies and the one that most often disappoints. The plant itself is not difficult; the pot is. In a few litres of compost, every slip in watering, feeding or weather shows up in the fruit.
The good news is that a balcony offers something an allotment does not. A roof or the balcony above keeps off the rain that spreads blight, and a wall gives back warmth in the evening. On a south or west-facing balcony a single cherry tomato plant can produce several kilos of fruit.
Sow balcony tomatoes indoors from mid-March to early April and move them outside once frost has passed and nights stay above 10C, usually late May or early June. Choose cherry, bush or trailing varieties, a pot of at least 10 litres for bush types or 20 for cordons, and six to eight hours of sun. Water evenly and feed with high-potash tomato feed once fruit sets.
When should you sow tomatoes for a balcony?
Sow indoors from mid-March to early April, roughly six to eight weeks before planting out.
Sow seeds about 5mm deep in seed compost and keep them warm, at 20 to 25C. They germinate in one to two weeks. When the first true leaf appears, prick them out into individual 8 to 10cm pots and move them to the brightest windowsill you have, at around 18C.
If you would rather not sow, garden centres and markets sell young plants from late April. Choose sturdy, dark green plants without yellowing lower leaves.
When can tomatoes go outside on a balcony?
Tomatoes cannot take frost and almost stop growing below 10C. In most of Britain they go out once the risk of frost has passed and nights stay above 10C, usually in late May or early June.
Harden plants off over seven to ten days: put them outside in light shade during the day and leave them out a little longer each time. Plants moved straight from a windowsill into full sun get pale scorch marks on their leaves.
When potting up, plant them deeper than they were, up to the first leaves. Tomatoes grow extra roots along the buried stem.
Which tomato varieties grow best in pots?
Small-fruited varieties are the safest choice. Cherry tomatoes ripen faster and more reliably than large beefsteaks, which in a pot often run out of summer before they colour.
- Cordon cherry tomatoes: varieties such as Sungold and Sweet Million grow up to 2 metres and crop all summer. They need a cane, regular side-shooting and a pot of at least 20 litres.
- Bush (determinate) varieties: stay at 40 to 80cm and need no side-shooting. Totem, Tiny Tim and Balconi Red are good examples, suited to small balconies and 10 to 15 litre pots.
- Trailing varieties: Tumbling Tom, red or yellow, spills over the edge of its container. Grow it in a hanging basket or railing planter at least 30cm across.
What size pot and compost do tomatoes need?
Bush varieties manage in 10 to 15 litres; cordon cherry tomatoes want 20 litres or more. More compost holds more water and nutrients and evens out the swings between waterings. The pot needs drainage holes.
Use a good peat-free compost for vegetables or tomatoes rather than garden soil, which slumps in a pot. Use fresh compost every year.
How much sun do tomatoes on a balcony need?
Tomatoes need at least six to eight hours of direct sun a day. They crop best on south, south-east and west-facing balconies. On an east-facing balcony with only morning sun they grow more slowly, and on a north-facing one they will not crop.
Do tomatoes need staking and side-shooting?
That depends on the variety. Cordon (indeterminate) tomatoes keep growing, so they are tied in and side-shooted. Bush and trailing types are left alone, because they flower on their side shoots.
- Push in a 150 to 180cm cane or spiral support when you plant, so you do not damage the roots later.
- Tie the stem every 20 to 30cm with soft twine, loosely, in a figure of eight.
- Once a week, pinch out the side shoots that form in the angle between the main stem and a leaf. It is easiest when they are 3 to 5cm long.
- In late July or early August, stop the plant by cutting off the top one leaf above the highest truss. It then puts its energy into ripening the fruit already set.
How often should you water tomatoes in pots?
Water evenly, so the compost never dries out completely and never stays waterlogged. In a July heatwave a potted tomato may need watering every day, sometimes morning and evening. Water the compost, not the leaves.
Uneven watering shows in the fruit. Blossom end rot, a dark leathery patch at the base of the fruit, appears when irregular watering stops the plant moving enough calcium into the fruit. Splitting happens when a dry plant suddenly gets a lot of water, after a thunderstorm for instance.
What should you feed tomatoes with?
Fresh compost is enough for the first three to four weeks. Once the fruit on the first truss starts to swell, feed weekly with a liquid tomato feed high in potassium (potash). Potash supports flowering, colour and flavour.
Too much nitrogen shows as a lush, dark green plant with few flowers, so general leafy feeds are the wrong choice in summer.
How do you pollinate tomatoes on a balcony?
Tomato flowers are self-fertile, but release pollen only when shaken, a job done by wind and bumblebees in the open garden. On an enclosed or glazed balcony there is often not enough of either.
When the flowers are open, gently shake the stem or tap the flower trusses around midday in warm, dry weather. Repeat every few days. Flowers can also drop because of heat above 30C or nights below 13C, whatever you do.
Which diseases affect balcony tomatoes?
- Blight: the most serious disease. Brown patches appear on leaves, dark streaks on stems, and the fruit turns brown and firm. It spreads in warm, wet weather, so the best protection is a roof or rain cover over the plant and watering at the base. Bin infected plants rather than composting them.
- Aphids and whitefly: on young shoots and leaf undersides. Wash them off with a firm jet of water or use an insecticidal soap.
When are balcony tomatoes ready to pick?
The first ripe cherry tomatoes usually come in July, with the main crop in August. Pick when the fruit is fully coloured and gives slightly when pressed. Do not keep them in the fridge, where they lose flavour.
When nights fall below 10C in late September, pick the green fruit too. In a paper bag at room temperature most ripen within one to two weeks.
What to do with balcony tomatoes month by month
| Month | Job |
|---|---|
| March | sow indoors from mid-month at 20–25C |
| April | prick out into pots, brightest window, last sowings early in the month |
| May | harden off; plant out at the end of the month if no frost is forecast |
| June | plant out in cooler areas, tie in, pinch out side shoots, start potash feed as fruit swells |
| July | water daily in heat, shake flowers, first fruit |
| August | main harvest, stop cordons, watch for blight |
| September | keep picking, bring in green fruit when nights turn cold |
Which herbs go well next to tomatoes?
Basil wants what tomatoes want: warmth, sun, shelter from cold and steady moisture. It belongs in the same corner of the balcony and on the same plate. See how to grow basil indoors on a windowsill and our balcony herb garden guide.
Tomatoes need a big pot on the floor; herbs do not. Basil, parsley, chives and thyme can go in a vertical garden without drilling standing right beside the tomato pots. The Urban Planty vertical garden clamps between floor and ceiling with a telescopic pole, adjusts up to 285cm and has nine pots, each with a 300ml water reservoir, so herbs need watering once or twice a week. It takes up less than a square metre of floor, on a balcony or indoors by a window, and costs €149 with free delivery.
Frequently asked questions
When should you sow tomatoes for a balcony?
Sow balcony tomatoes indoors from mid-March to early April, six to eight weeks before planting out. Tomato seed germinates in one to two weeks at 20 to 25C.
When can tomatoes go outside in the UK?
Tomatoes can go outside once the risk of frost has passed and nights stay above 10C, usually late May or early June in most of the UK. Harden them off for a week first.
What size pot do tomatoes need?
Bush tomatoes need a pot of at least 10 to 15 litres, and cordon cherry tomatoes 20 litres or more. The pot must have drainage holes.
Should you remove side shoots from cherry tomatoes?
Remove side shoots only from cordon cherry tomatoes, weekly, when they are 3 to 5cm long. Bush and trailing tomatoes such as Tumbling Tom are not side-shooted.
Why do tomatoes go black on the bottom?
A dark patch on the base of a tomato is blossom end rot, caused by a lack of calcium in the fruit when watering is irregular. Water tomatoes evenly and mulch the pot.
