Planting onions from seeds will result in an economical method for onion production. Onion growth and bulb size are fully dependent on the length of the summer days. Long-day varieties of onions may produce the largest of the bulb varieties. According to the University of Minnesota Extension Service, the bulbs begin to form when day length approaches 14 hours to 16 hours. In most cases, this may include only the Northern portion of the country. Full sun exposure, climate and onion variety will play a large part in onion seed propagation.
Prepare the onion seed bed as early as the local climate will permit. Typically, the ground should be free of any frost or freezing conditions. Layer 1 1/2 inches of organic material onto the onion seedbed. Organic material will range from rich compost humus, which is the best, to turning under a green manure cover crop.
Work the organic material into the soil to a depth of at least 8 inches. Dig the material into the soil using a shovel, or run a rototiller over the onion growing bed. The goal is to incorporate the organic material thoroughly with the soil.
Smooth the onion growing bed with the garden rake. Remove any rocks or organic debris that may cause the onions seeds from germinating. Large pieces of material that lay on the onion bed surface may cause the seeds not to break through the soil.
Make the seed-planting rows with the handle of the garden rake. The rows should be approximately 8 inches to 12 inches apart. The depth of the row furrow can range between 1/2 inch deep to a full 1 inch.
Plant the seeds approximately 1 1/2 inches apart from each other. Cover the seed with soil to a final depth that ranges with the depth of the furrow, 1/2 inch to 1 inch deep. Keep the seeds moist, but not overly wet. Do not allow the onion bed to dry out.
Thin the onions plants, to 3 inches apart, when the green leaves range from five leaves to 10 leaves. Use the young pulled onions as scallions.
Keep the onion bed weed-free throughout the season.