During Cal’s journey in Jedi: Fallen Order, he will encounter unique wild and plant throughout the galaxy. Sometimes, he’ll locate small seeds of these plants that he can take with him and add to the Mantis.
Locating the seeds takes a bit of time. You’ll need to go out of their way to find them by going off the traditional path of the game and start exploring a planet. BD-1 will comment about how Cal is going the wrong way when this happens, which is a good thing for players looking to find secrets.
Seeds are sometimes found in chests, or on larger plants that BD-1 can scan. Cal takes the small sample and add it to his collection. They do not immediately go back to the Mantis, though. Cal needs to bring them back and plant them himself.
To plant seeds in the terrarium, have Cal approach the small, protected environment next to the kitchen inside of the Mantis. It is to the left when players exit Cal’s private room at the back of the Mantis. Walk up to it and hit the right stick on your controller to access it. When you arrive, you should see the notification of a new plant getting added to it.
There is no gameplay benefit or bonus for acquiring all of the plants, but you will receive the “Green Thumb” achievement for completing the collection and having a fully grown terrarium.