This achievement is gained once you have successfully created a flower pot and placed it. This must be done in survival mode. This can be done on any difficulty.
You must begin by collecting at least three clay. Clay blocks are commonly found underwater. They look like this:
Once you have at least three clay go to a furnace. Cook three clay in the furnace to produce three clay bars. Then, go to a crafting table and craft a flower pot.
Place the flower pot on any block. Place a flower or shrub in the pot and your achievment should unlock.