First dye rice green for 'grass' Then, find dirt without fertilizer for the garden.
You could add in farm related materials including animals, a barn, fencing, gardening tools, vegetables, tractors, or a silo
Tools for pouring like measuring cups, spoons, shovels, and buckets are all great additions.
Have your child help you put the bin together. You can even make up a story about each animal or the entire farm as you put everything in.