Container sizes for terrace crops
Grow more on your terrace.
Undersized containers are the most common reason terrace crops underperform. The soil volume determines how much water and nutrients roots can access between waterings, and how much buffer the plant has during heat spikes.
As a working guide: lettuces and radishes do fine in containers 15 cm deep and 6 litres in volume. Herbs need at least 20 cm depth. Courgettes, aubergines and peppers need 30 cm depth and 15 to 20 litres per plant. Compact tomatoes want at least 40 cm depth and 20 litres; full-size indeterminate varieties need 50 litres or more, which is rarely worth the weight on a terrace.
Weight matters too. Wet potting mix weighs roughly 0.6 to 0.8 kg per litre. A 40-litre tomato container at field capacity weighs around 30 kg before you add the pot and water reservoir. Check your terrace load rating before scaling up, and cluster heavy containers over structural beams where possible.