"Winter onion" is the name given to an extraordinary onion plant that is unlike most other onions known to the average gardener. It’s also known by more descriptive names, including the Egyptian walking onion, tree onion, top onion, and perennial onion. It’s called an Egyptian walking onion because it "walks like an Egyptian" around your garden, planting and replanting itself.
The winter onion is an extraordinarily hardy plant, growing easily in Zones 3-9. In newly planted winter onions, a bulb grows on top of each of the stems produced. After the first year, onions burst forth out of these bulbs, at the top of the stem! This cluster of onions at the top of the plant is called a topset. It looks like an odd little tree, hence the term “tree onion.” When the onions become to heavy, they bend all the way to the ground and replant themselves a bit further away from the original plant, hence the term “walking.” It seems to walk away from
Find a spot in your garden that receives a lot of sun. Take your offset and insert it about 2” deep into well-draining soil that is a little damp. You’re going to be planting the onions in rows that are about 12 inches apart. Plant the onions offsets about half a foot apart from each other. If you wish, you can also plant the onions in clusters.
If you were to plant the onion’s offsets in spring and summer, they would probably grow nice full leaves and start to develop strong bulbs and roots below the surface, Since this would their first growing season, however, you probably wouldn’t get to see any cool topsets that year.
They don’t require much water at all, but are adversely affected by weeds, so make sure to weed the area around your onions vigilantly.
The best time of year to plant the onions is fall. They’ll be able to settle into the ground and form a really nice root system in time for spring’s growing season. You won’t see any offsets.
You can even plant the onions during winter, but only if the ground isn’t frozen or have snow.