Leek is very easy to start on water for growing on hydroponics afterwards.
From kitchen scraps, use a piece of leftover leek. Just the bottom part, the leaves cut off.
Place in a shallow dish of water. Refresh the water daily to avoid rot.
After 2 days, roots appear and the leaves have started growing:
After a few more days, roots are growing well. Two weeks later the plant can ban be transplanted in clay pellets and watered with nutrient solution.