quickest out of all planting methods and produce larger than natural bulbs. Onion Seeds: seeds of the white onion that can be planted into sets in late Spring. While this method may have the longest grow time (up to 4 months for mature bulbs), the onions produced are the least susceptible to disease. Different varieties of onions vary in the time of year at which a mature white onion is cultivated: Short-day onions are onions that form bulbs when they are in an environment where they get 10 to 12 hours of sunlight a day. Intermediate day onions are onions that will form mature bulbs when they are in an environment where they get 12 to 14 hours of sunlight a day. Long-day onions are onions that form bulbs when they are in an environment where they get 14 to 16 hours of sunlight a day. For most white onion varieties, a soil pH of 6-7 is optimal. At times when the pH of the soil for onions is below 5.5, magnesium and molybdenum supply is inadequate and at a pH of above 6.5, zinc, manganese and iron are less present in the soil. References Onion cultivars