葱坊主の英語訳を探したら、onion headが見つかった。玉葱も同じように茎を伸ばして花を咲かせるので、それと区別してgreen onion flowerとかwelsh onion flowerとでも呼びたいものだが。

Onion head is found when looking for English translation of the Negibouzu. Since onions also blossom just as stretched stems, I want called green onion flower or welsh onion flower in distinction from onion.