i search some pictures for potting soil, why are some have pebbles?
Pebbles aid in draining excess water away from the roots of plants.
They are probably nutrients and vermiculite and perlite as someone else said which is just added to help the flowers to be more healthy and to produce.
If the pebbles are white then it is actually vermiculite and perlite. They help water and air to get to the roots of the plants.
