Suitable containers are anything that is porous or has drainage holes and can hold compost/coir. Watch out for paper or cardboard-based containers as they may collapse when they are too wet or suck away moisture from the seedlings’ roots when dry. If you don’t want to spend money on purpose-made containers use yoghurt pots, the base of plastic milk bottles, and mushroom or fruit trays (check they have drainage holes in the bottom and clean them thoroughly).
Getting the correct size of container is crucial and it varies for different vegetables. If you put a seed in a container that is too small its growth will be stunted, it could dry out quickly and die. You will move most of these vegetables into bigger pots as they grow, but here’s a quick guide to correct container sizes for when you first sow the seeds:
Suitable for a shallow container 3-5cm deep
Lettuce, Kale, Radish, Cabbage, Spinach, Beetroot, Pepper, Tomato, Aubergine, Onion seeds