To plant celery from seed, fill a container – a tray or pot – with seed compost. Celery seeds are particularly fine and can be difficult to handle; lightly sow the seed across the surface of the compost – it may be easier to take a pinch of seed at a time.
Water by standing the container in a saucer or larger tray of water, enabling the water to soak up into the compost, rather than pouring in from on top to disturb the seeds. Cover with a thin layer of vermiculite and place the pot or tray in a location with constant warmth. A heated propagating matt is ideal, although you could alternatively use a windowsill or a greenhouse.
Keep the compost moist, and don’t let it dry out. If you are using a propagator, remove the seedlings once germinated. When the seedlings have formed leaves they need to be potted on.