Choose a firm, healthy onion with an intact root end
Cut off the top, leaving the root end intact
Place the root end in a shallow dish of water
Keep the root end partially submerged
Put the dish in bright indirect light
Change the water every 1 to 2 days
Wait for green shoots to appear
Transplant the rooted onion into soil when roots and shoots are established
Plant it root-side down with the top just below the soil surface
Water the soil lightly and keep it evenly moist
Place the plant in full sun
Harvest green tops as they grow
Let the bulb mature if you want a full onion
Pull the onion when the tops yellow and fall over