noun
onion flower head; scallion flower bud
Refers specifically to the round flower bud that forms at the top of a green onion or scallion stalk. Often used in cooking or gardening contexts.
ネギ坊主ができると、ネギが硬くなる。
When the onion flower head forms, the green onion becomes tough.
畑にネギ坊主がたくさん咲いている。
Many onion flower heads are blooming in the field.
ネギ is the green onion plant itself, while ネギ坊主 is specifically the flower bud that appears on it.
Compound of ネギ (green onion) and 坊主 (monk, shaven head), from the resemblance of the round flower bud to a monk's shaven head.