SCALLIONS, also known as bunching onions, are simply young onions that have not formed bulbs yet. Like other onions, they prefer well-drained soil and full sun. You can grow them from seed, from "onion sets" (small bulbs) or from purchased seedlings.
To start scallions from seed, sow seed indoors in early spring eight to 10 weeks before your last frost date. You can grow scallions from any type of onion seed, however, varieties sold as scallions or bunching onions usually yield the best results. Sow the seeds thickly in a small pot or seed flat (up to 50 seeds in a 4" x 6" flat). As the plants grow, use scissors to trim back the grassy growth and keep the plants 3" to 4" tall. Set the seedlings outdoors a week or so before your last frost date, carefully teasing apart the roots and setting the plants about an inch apart.
To start from sets, look for them at garden centers in early spring, usually sold by the pound. You can choose any type and color you want — red, yellow or white. Plant them about an inch apart and 1-1/2" to 2" deep.
To start from seedlings, look for them in spring, sold in bundles of 50 to 75 plants. You can order them from mail-order nurseries. Your local garden center may carry them, as well. Plant them as you would seedlings you grew yourself.
Scallions have shallow root systems, so keep the plants evenly watered. Weed the bed frequently to minimize competition for water and nutrients. Begin harvesting your scallions when the plants are about the size of a pencil. Sow successive crops for a continuous harvest.
Related article: Onions 101, includes a slideshow on planting onion seedlings