Growing Tomatoes in Pots, Step by Step
Tomatoes are the crop most people try first and the one that most often disappoints in containers. The gap between a plant that gives 3 kg and one that gives 300 g is almost entirely down to four decisions made in the first three weeks.
Step 1: Choose the right type
Tomatoes come in two growth habits, and this matters more in a pot than anywhere else.
- Determinate (bush) varieties grow to a fixed size, set fruit over a few weeks and stop. Compact, tidy, need minimal pruning, ideal for containers. Examples: 'Balconi Red', 'Tumbling Tom', 'Totem', 'Vilma'.
- Indeterminate (vining) varieties keep growing until killed by frost, producing over a long season. Higher total yield but need tall, strong support and regular pruning — a 2 m cordon on a windy balcony is a liability.
For a first container tomato, pick a determinate or dwarf indeterminate variety bred for pots. Cherry and currant types are more forgiving than large beefsteak types, which crack and need near perfect conditions.
Step 2: Container and support, from day one
Minimum 25 litres for a determinate variety; 30–40 litres for an indeterminate one. One plant per container — two tomatoes in one pot compete and both produce less.
Install the support at planting time, not later. Pushing a cane in beside an established plant damages roots. Options: a single 1.5 m bamboo cane for determinate types, a sturdy spiral stake, or three canes with string wound between them. Hanging baskets suit trailing varieties like 'Tumbling Tom', which need no support at all.
Step 3: Plant deep
Tomatoes root along any buried stem. Strip the lowest leaves and plant the seedling up to its first true leaves — burying 5–8 cm of stem. That buried section becomes extra root mass and makes the plant markedly more stable and drought-tolerant. Do this and you will never need to stake as heavily.
Use fresh potting mix with 20% perlite, plus a handful of slow-release feed. Fill to 3 cm below the rim so there is room to water.
Step 4: Water consistently above all
Tomatoes punish irregular watering. A dry spell followed by heavy watering causes fruit to split and leads to blossom end rot, the black leathery patch on the bottom of the fruit. That condition is a calcium uptake problem caused by water fluctuation, not a calcium shortage in the soil.
In practice: check daily, water when the top 3 cm is dry, and in hot weather expect to water a 25 L pot once or twice a day. Mulch the surface to slow evaporation. A self-watering container or a reservoir spike makes a measurable difference here.
Step 5: Feed on the fruiting switch
Use a balanced feed while the plant is growing vegetatively. The moment the first flower truss opens, switch to a high-potassium tomato feed and apply twice weekly at the label rate. Underfeeding at this stage is the most common reason container tomatoes set few fruit.
Step 6: Feed the flowers
Outdoor tomatoes are usually pollinated by wind and insects without help, but on a sheltered balcony or behind glass, pollination can fail. Two cheap interventions: tap or gently shake the flower trusses around midday, or use a soft brush to move pollen between flowers. Do this daily while flowering. If flowers drop without setting fruit, check temperature — above about 30 °C or below 13 °C, pollen becomes non-viable and fruit will not set regardless of what you do.
Step 7: Prune by type
- Determinate: remove only yellowing leaves and any shoots below the first flower truss. Do not prune the growing tip — that is where the crop is.
- Indeterminate: remove side shoots (suckers) that appear in the leaf axils, pinch them out when 3–5 cm long, and stop the plant at the height you can support by pinching out the top about a month before first frost.
Problems you will probably meet
| Problem | Cause | What to do |
|---|---|---|
| Black patch on fruit base | Blossom end rot, uneven watering | Stabilise watering; remove affected fruit; later fruit usually fine |
| Fruit splitting | Sudden heavy water after dry spell | Mulch, water evenly, pick fruit slightly early |
| Leaves curling upward | Heat or water stress, or a virus | Check moisture first; if persistent and plant is stunted, remove it |
| Flowers drop, no fruit | Temperature outside 13–30 °C, or no pollination | Tap trusses daily; wait for suitable weather |
| Lower leaves yellowing | Normal ageing, or nitrogen shortage | Remove yellowed leaves; feed if it is widespread |
| White powdery coating | Powdery mildew | Improve airflow, water the mix not the leaves, remove worst leaves |
Harvest and end of season
Pick when fruit is fully coloured and slightly soft. Regular picking encourages more to set. At season end, when night temperatures drop below 10 °C, pull the plant, compost the green material and replace the mix — do not reuse it for tomatoes next year. Container-grown tomatoes ripen unevenly; any large green fruit at the end can be brought indoors to ripen on a windowsill, or made into chutney.
Common questions
Why are the bottoms of my tomatoes black?
Blossom end rot, caused by irregular watering preventing calcium uptake, not by a lack of calcium in the mix. Stabilise watering and mulch; fruit set later is usually unaffected.
How many tomatoes should one plant produce?
A well-grown dwarf container variety yields 1.5 to 3 kg over a season. Less than about 500 g usually indicates insufficient container volume, inconsistent watering or inadequate feeding at fruit set.
Should I remove the yellowing lower leaves?
Yes, once they are fully yellow. Snap them cleanly at the stem. It improves airflow around the plant, reduces disease pressure and directs energy into fruit rather than ageing foliage.