In a large mixing bowl, combine all of the dry ingredients (baking soda, citric acid, corn startch, and sea salt) and stir well.
In a small bowl combine the carrier oil, vanilla extract, essential oils, and natural dye if using.
Slowly add the wet ingredients to the dry mixture and work it together with your hands until its crumbly.
Add in the dried flowers or herbs if using.
Spritz the witch hazel or water onto the bath bomb mixture, mixing well with your hands to combine. Do this just until the mixture holds together when squeezed without crumbling. It should feel like wet sand. You may need to add slightly more witch hazel if it hasn't achieved this consistency yet.
Firmly press the bath bomb mixture into silicone molds, muffin tins, ice cube trays, or bath bomb molds.
Gently turn the molds over onto a flat surface to remove the bath bombs and allow to dry for 48 hours, or until hardened.
Storage: Keep the bath bombs in an airtight container away from moisture.