In each Inn throughout the game there will be a magic pot as you enter, which requires seeds. You can get a variety of seeds from Bronze all the way upto Rainbow. Seeds are dropped by enemies and also can find them while exploring the world.
Each seed planted will give a random reward and give exp to the pots level, once it hits the maximum of level 5 you will get the achievement.
•Will likely get enough seeds naturally by just playing the game
•Each level up increases the drop rate from enemies and also increases the chance of better loot
•Magic Pot level remains when starting a new game plus
•You can unlock abilities in the luck tree for increasing item drop rate from enemies if you want to grind for seeds (But this shouldn't be necessary)
•Often worth saving your higher quality seeds until the pot is max level to then have the highest chance of the best loot
#Planting your first seed will also unlock the 'Gardener' achievement