Onions are planted either from seeds, plants or dormant bulb sets. Seeds take the longest amount of time to grow, while gardener's save time by planting onion sets which are widely available in the early spring. Planting the sets at the proper depth and spacing is essential to increase the onion size and quality.
Plant onion sets, or dormant bulbs, 1-½ to 2-½ inches deep in a location with full sun. Onions require well-drained soil high in organic matter and consistent moisture.
Space the sets 3 to 4 inches apart in rows. Leave a space of 12 to 15 inches between rows. Harvest every other plant after a month and a half to use as scallions, also known as spring onions.
Thrips, onion maggots and soil-borne diseases are common among onion plants. Avoid problems with these pests by planting onion sets in a different location each year. Keep the onion sets free of weeds and mulch with grass clippings or straw to help keep the soil moist.