PS4 trophies made an excellent video listing all the plants and it's locations; just remember that you need to plant each seed you find to make them grow. After all of them are full grown, you'll get the achievement.
Edit: as some players commented, the distance between the player and the ship, while a plant is left "growing", may be a factor for it to grow faster. It doesn't matter if it's while playing the regular story or post-story while trying to get other achievements (which was my case). I made grow at least 4 plants while traveling to Zeffo and Bogano, moving a little far from the ship, kill some troopers and going back to the ship to check (for me, Bogano has the least "complicated" route to return to the ship if you stray to far from it).