This still stumps people, and it is easy to see why. They look so similar! Okay, that’s an understatement; the leeks and green garlic are undistinguishable visually. The onions are the easiest to tell from the others, as the green part of the stalk is tubular and hollow. The green part of the garlic and leeks both form the same “V” shape when cut crosswise, and the leaves of both have a kind of left-right fan structure, so that’s no help either. You have to use your nose. Scratch ‘n’ sniff. The green garlic will smell like garlic. But take comfort in the fact they are all in the same family (the alliums), so in a lot of cases if you accidentally ended up using ‘the wrong one’ in a recipe [potato-green garlic soup instead of potato-leek soup, for example], it is not like you will suddenly have something inedible! It may be different, but will taste just fine.