The word vegetable in Japanese is yasai (野菜). In this reference I offer simple definitions, translation, and pronunciation to help you learn more about vegetables in Japan (and the Japanese language).
Negi is scallions (a Welsh onion) — a Japanese leek, very similar to, and often mistaken for, green onions. It is an ingredient found in heaps of Japanese dishes such as ramen, donburi, shabu-shabu, and even on beef tongue in yakiniku!
Here’s a video showing negi being farmed. Sorry, it’s in Japanese, but it’s the best I could find. I think you can still learn a bit from it visually.