Celery can be planted with soil or without soil as well. For the first approach, you only provide lots of water to the base of the plant. Use a bowl of warm water for that. Change the water every two days. Use spray to keep the top part of the base moist. New leaves will grow after a few days.
In the other approach, providing lots of water is also necessary. Fertilize regularly and add plenty of mulch compost around the plant. This is for retaining lots of moisture for the plant. Celery is a heavy feeder. With no water and nutrients, the stalks will shrink. When the leaves stalks grow, tie them to keep them from scrawling.