Allium plants such as chives are grown for their green foliage. The slender, grass-like leaves are cut back for culinary use anytime during the growing season. Cutting the leaves encourages new growth.
Allium plants such as onions and garlic are primarily grown for their mature bulbs. The leaves or foliage remain on the plant through the growing season. When the foliage turns yellow, dies and bends over, bulbs are ready for harvest. The bulbs are dug up and stored in a shady, dry place. When the bulb necks dry in a week or two, the foliage is cut off 1 inch above the bulbs.
An old-fashioned method of storing onions or garlic is to weave their intact tops together and make braids of the bulbs.