(Allium fistulosum). This is a perennial onion that has numerous common names including the Welsh onion, green onion, spring onion and scallion. It has hollow leaves and does not form a bulb as do immature, thickly planted bulbing onions (Allium cepa) that are also called green onions, spring onions and scallions. Japanese bunching onions grow in U.S. Department of Agriculture plant hardiness zones 6 through 9.
Germination: The minimum temperature for onion seeds to germinate is higher than for most vegetables that grow through the winter, and they grow slowly when they are young. You can seed Japanese bunching onions in March after the danger of frost has passed through mid-August. The seeds will germinate at temperatures between 46 and 86 degrees F, but germinate best at temperatures over 60 F. Plant 12 seeds per 1 foot along each row, 1/4 to 3/4 inch deep. The seeds should germinate in six to 12 days. Thin to 3 to 4 inches between seedlings.
Sow in spring for summer use or sow in fall for overwintering. Little or no bulbing. If your winters are severe, this is the one to grow. May be handled as a perennial by dividing the clumps the second summer to produce a new crop.