Container Sizes for Tomatoes, Peppers and Herbs

Pot size is the most consequential decision in container growing, and it is usually made in a garden centre in about four seconds. Here are the numbers worth knowing first.

Why Container Volume Matters More Than Width

Nurseries sell pots by diameter, which tells you almost nothing useful. A 30 cm (12 in) pot can hold anywhere from 10 to 25 litres depending on how deep and how tapered it is.

What plants actually respond to is volume of compost, because volume determines two things: how much water is held in reserve, and how much nutrient buffer sits between weekly feeds. Double the volume and you roughly double the time before a plant hits stress on a hot day.

Undersized pots rarely kill outright. They produce a slower, half-size plant that flowers late and needs watering twice a day. That is the real cost.

Tomatoes: 40-75 Litres for Indeterminates

Indeterminate (cordon) tomatoes are vines. They will run to 2 m (6 ft) or more and carry fruit for months, and their root systems want the room.

Give an indeterminate variety 40 L minimum, and 50-75 L if you want to water once a day rather than twice in August. One plant per pot — two in a 40 L container will compete and both will underperform.

Determinate (bush) tomatoes stop at a set height and finish faster, so 25-30 L is workable. Dwarf and micro-dwarf varieties such as 'Red Robin' will genuinely crop in 8-10 L.

Depth matters here more than for most crops. Tomatoes root deeply and will also root from buried stem, so aim for 35 cm (14 in) or more and plant them deep, burying the lower third of the stem.

Peppers and Chillies: 15-25 Litres

Peppers are less thirsty than tomatoes but no less fussy about consistency. Wildly swinging moisture is what causes blossom end rot and bud drop.

Sweet peppers and larger chillies want 20-25 L. Compact chillies such as 'Apache' or most ornamental types crop well in 12-15 L. Depth of 25-30 cm (10-12 in) is plenty; peppers root wide rather than deep.

Herbs: Small Pots, Big Differences

Basil is a soft annual that transpires heavily and hates drying out — give it 5-8 L, not the 0.5 L supermarket pot it arrived in. Coriander and dill bolt when stressed and want depth for their taproots, at least 25 cm.

Mediterranean perennials are the opposite. Rosemary, thyme, oregano and sage prefer to run slightly dry and will rot in a large, constantly damp pot. Give them 5-10 L, gritty compost and full sun.

Mint, lemon balm and tarragon spread aggressively by runners. Always give them their own container, 10 L or more, and never plant them alongside anything you care about.

Parsley is biennial with a genuine taproot: 20 cm depth minimum, ideally more.

Depth Rules of Thumb by Root Type

Material Changes Everything About Watering

Two identical 25 L pots in the same spot can need water on completely different schedules depending on what they are made of.

• Terracotta breathes and evaporates through the wall. Expect to water 30-50% more often. Excellent for rosemary and thyme, punishing for basil.
• Glazed ceramic and plastic hold moisture longest. Best for tomatoes, peppers and anything you cannot check daily.
• Fabric grow bags air-prune roots and give superb root structure, but they dry fastest of all. In a hot, exposed spot a 40 L bag can want watering twice a day.
• Metal heats up badly in direct sun and can cook roots at the pot edge. Line it or shade the sides.

Colour matters too. A black plastic pot in full afternoon sun can push root-zone temperature past 35C, at which point tomato roots stall. Light-coloured pots, or pots placed to shade each other's sides, fix it cheaply.

Once your pots are sized, the next constraint is light — check how much sun vegetables really need before committing to fruiting crops. The balcony starter guide covers soil mixes and feeding.

Rather than tracking litres, depths and feed intervals in a notebook, you can let Vegarden hold your container list and tell you what fits where and when each pot needs water.