Onion seeds are often extraordinarily rare items that are used to cultivate Onions after being planted into the ground.
In fanon games
Below this point is where users place their version of Onion seeds.
In Pikmin: Connection of the Worlds
This article or section presents information pertaining to Pikmin: Connection of the Worlds, a fanon game created by PikFan23.
Onion seeds are a very special type of seed in Pikmin: Connection of the Worlds, as they can grow entire Onions. Various Onion seeds are scattered throughout the world and can be collected to grow an Onion of a matching color. The only place they can be grown is at the Garden, which, unfortunately, is nearly devastated because of the Great Volcano. Purple Pikmin, White Pikmin, Green Pikmin, Cyan Pikmin, Burgundy Pikmin, Brown Pikmin, Gray Pikmin, Silver Pikmin, and Tan Pikmin all have corresponding Onion seeds, but Red Pikmin, Yellow Pikmin, and Blue Pikmin do not, as they already have their Onions. There is no Bulbmin Onion seed, as Bulbmin are stored in the Ship.
To obtain an Onion seed, one must defeat the boss of more challenging caves and collect the upgrade treasure it held. Then, the cave must be entered again to face a new boss in place of the previous one. Once it is defeated, it will drop the Onion seed. Also after that boss is defeated, it and the boss previous will alternate with each visit.
After having collected an Onion seed and restored the Garden, several spots on the ground will visibly glow. A humorous cutscene will unfold upon visiting the location, where the Research Pod will go to a spot, and then flip upside-down to eject the seed into the ground. The Garden must be visited for four more consecutive days after this for the seed to be able to grow. If another area is visited instead, the seed will be destroyed, necessitating having to collect another seed from the boss it was initially obtained from. Additionally, several Onion seeds can be planted at once.