How to Grow Tomatoes in Containers

Container tomatoes fail for one reason: the pot is too small. Get the volume right and the rest is straightforward.

Minimum pot size

A 10-litre pot will keep a tomato alive but not productive. Anything under 15 litres needs watering twice a day in summer.

Soil mix

• 60% multipurpose compost
• 20% garden soil or loam — adds weight and buffers moisture
• 20% perlite or coarse grit for drainage
• Slow-release fertiliser mixed in at planting
• A handful of crushed eggshell or lime to prevent blossom-end rot

Do not use garden soil alone — it compacts in a pot and drains badly.

Watering

Inconsistent watering is the cause of blossom-end rot, not calcium deficiency on its own. The plant cannot move calcium without steady moisture.

• Water when the top 3 cm is dry — check with a finger, not a schedule
• In peak summer a 25-litre pot may need water twice a day
• Water slowly until it runs out of the drainage holes
• Never let the pot stand in a saucer of water — roots rot
• Mulch the surface to slow evaporation

Feeding

Compost nutrients run out after about 6 weeks. From then, feed weekly with a high-potassium tomato feed once the first flowers set. Too much nitrogen before that gives you leaves and no fruit.

Support

• Determinate: a single stake or a small cage is enough
• Indeterminate: a tall stake or string, and pinch out side shoots weekly
• Put the support in at planting, not later — driving a stake through the root ball sets the plant back

Best varieties for pots

Common problems

• Blossom-end rot — black patch on the base. Inconsistent watering. Remove affected fruit and stabilise watering.
• Yellow lower leaves — usually nitrogen depletion or waterlogging.
• No fruit, lots of leaf — too much nitrogen, too little sun, or nights too cool.
• Split fruit — a sudden heavy watering after a dry spell.

Common questions

What size pot do tomatoes need?

At least 15 litres for a cherry or determinate variety, 25-30 litres for a standard, and 40+ litres for an indeterminate cordon.

How often should you water tomatoes in pots?

When the top 3cm of soil is dry. In peak summer a 25-litre pot may need watering twice a day. Consistency matters more than frequency.

Why are my tomatoes getting black bottoms?

Blossom-end rot, caused by inconsistent watering rather than calcium deficiency alone. The plant cannot move calcium without steady moisture.

Can you grow tomatoes in a 10 litre pot?

You can keep the plant alive, but it will not crop well and will need watering twice daily in summer. 15 litres is the practical minimum.