Allium cepa, or the common onion, is a member of the lily family. It is a cool-season vegetable. The plant requires five to six months of growth before harvest. The plant will start by forming a top, and then it will sprout a bulb. Allium cepa are either long-day or short-day onions. Long-day onions require 15 hours of daylight. Short-day onions require 10 hours of daylight.
Plan to grow your onion in a location that has rich, loose, well-draining soil. If your soil is not loose and/or full of organic matter, work compost into it with a pitchfork.
Prepare your growing site by making bed rows that are 16 to 20 inches wide. Hill-up the rows with dirt to a height of 4 to 5 inches. The length of your rows is a personal decision. Space your rows 12 to 18 inches apart.
Use the end of a shovel or other garden tool and run it down the length of your rows to make ½-inch furrows.
Set seeds into the furrows 3 inches apart.
Use a rake to cover the furrow and seeds with dirt.
Gently water your rows. Do not over-water or you will wash your seeds out.
Spread 2 to 3 inches of compost or organic mulch over your rows.
Water every seven to 10 days.
Feed your rows with a low nitrogen fertilizer such as 5-10-10 every 8 to 10 weeks. The amount of fertilizer should be determined by reading the manufacturer's instructions. Water the rows gently before and after fertilizing.
Watch for the top of the plants to dry out and fall over. This is the sign that the plant is ready for harvesting.
Harvest by pulling at the base of the dead foliage. The bulbs should easily lift from the ground. Lay the onions in a shady outdoor place for 24 to 48 hours. This will help them dry.
Remove the onions from the shady area and bring them indoors.
Store onions in a well-ventilated, dry and cool area.