Green onions are sometimes called scallions or spring onions. They are commonly used in Asian cuisines, but may also be found in recipes in many other cuisines. Green onions have a sharp onion flavor, with the white part being more strongly flavored than the green. There are several vegetables and herbs that can be used in place of green onions, but choose carefully. Some work better in raw dishes, and some work better when cooked. Choose the appropriate substitute for your intended use.
Leeks have an appearance similar to a fatter green onion, but their flavor is not the same. Leeks have an intense onion flavor, and a rich depth that green onions lack. They are an appropriate substitute for green onions in cooked dishes, but they are too tough and intensely flavored to work well raw.
Shallots are small dry onions with a fresh onion flavor. Use them as a substitute for green onions in cooked dishes, or use very finely minced shallots sparingly in raw dishes. Their flavor can be very pungent when used raw, so add raw shallots very lightly, then taste the dish and adjust the amount used to suit your tastes.
Ramps are also known as wild leeks. They are found wild around the Appalachian Mountains and surrounding states. They are intensely flavored and taste like an onion and garlic hybrid. Their flavor is extremely strong, so they should only be used in cooked dishes.
Substitute fresh chives for green onions in raw dishes. Chives have a very mild onion flavor that is similar to the green section of a green onion. They will work in cooked dishes, but their flavor will become very mild. They are more appropriate in dishes where they will be used raw. Do not use dried chives unless you have no other option, because their flavor changes dramatically when dried.
References and ResourcesThe Cook's Thesaurus: Green Onions & Leeks
The Cook's Thesaurus: Dry Onions and Shallots
All Foods Natural: Chives