In a spice grinder, grind the dried lavender for 30-40 seconds. This step may be skipped if a spice grinder isn't available.
In a large mason jar (8 ounces or quart-size), add the baking soda, diatomaceous earth, ground dried lavender, and lavender essential oil . Secure the lid and shake the ingredients together until combined. Store the sealed jar at room temperature until needed.