To grow onions hydroponically, you must first prepare large, healthy and plump onion balls, peel off the rotten skin, and cut off the poorly growing or too messy roots at the bottom. Prepare a transparent hydroponic container, fill it with clean water and then put the onion on it. It is best to let its roots just touch the water. At the beginning, the water should be changed every day. After small roots grow, the water can be changed every other day. When green shoots grow on the top, the water should be changed every 3-4 days.