What is the proper way to plant onion sets?
Before planting sets, separate the bulbs into two size groups -- those smaller than a nickel in diameter and those larger than a nickel. The larger sets often bolt (produce a flower stalk) and don’t produce good-sized bulbs. Use the larger sets for green onions. The smaller sets can be allowed to develop into mature onions.
Plant sets in early spring as soon as the ground can be worked (typically late March to mid-April in Iowa). Sets should be planted at a depth of 1 to 1½ inches in rows 12 to 15 inches apart. For dry onions, plant sets 2 to 3 inches apart. Sets grown for green onions can be planted closer together.