You will not need to unlock any crafting-recipe to make them. Instead, Adobe Bricks can be obtained by putting Mud into a Forge with some Fuel to harden 1 block of Mud into 4 Adobe Bricks each. Adobe bricks can either be placed as they are like any building-block, but can also be used as a material to craft more refined Adobe building-blocks. Upon crafting/taking Adobe Bricks for the first time, the recipe for Flower Pots is automatically unlocked. You can find Mud in the Stalactite layer underground, but also as a lakebed and riverbed on the surface of any Creativerse-world.