Green onions are small onions that are harvested young and used for their slender white bulbs and green stems. They're also called scallions, onions with blades, or bunching onions.
Green onions can be grown from many types of onions. They may be grown from seeds or from transplants called onion sets. The onion varieties you choose can include onion types that only mature as green onions, or you can simply harvest the bulb-forming types when they are young.
Plant onion sets or sow onion seeds as soon as the ground can be worked in the spring. Onions prefer soil that is loose and well drained.
Sowing onion seeds is the least expensive option, but it takes the longest. Seeds may not germinate, and weeds can be a problem. Pulling weeds may also pull up tiny onion seedlings. Sow onion seeds in a full sun location and cover with about 1/2 to 3/4 inch of soil, keeping the soil evenly moist but not waterlogged.
Planting onion sets is the easier method. Onion sets are seedlings that were started the previous year, harvested and kept dormant through the winter, then sold in bunches in the spring. Plant onion sets in full sun, with each onion plant 1 to 1-1/2 inches deep.
Because they're harvested while still young, green onions can be planted fairly close together, about 1 to 2 inches. If you are growing the onions longer to form bulbs, space them 2 to 3 inches apart. You might want to harvest every other green onion and leave the rest to grow and mature.
How do you know when to harvest green onions? That's up to you. You may only need to grow onion sets for a couple of weeks to a month before pulling them out.
If you are only wanting to use the green tops of scallions, try regrowing the greens with this trick. The foliage can be easily regrown from the white bulb. Place the white bulb, roots down, in a glass or jar with just enough water to cover the roots. Place in a sunny location. Change the water every couple of days. You can reuse the green leafy parts for a couple of weeks until they start to lose flavor.