In a wide mouth container combine baking soda, peroxide, castile soap, and essential oils, stirring well.
You'll want to make a fresh batch each time you need to use it. I would not try to make it ahead and store indefinitely. This is one natural cleaner that works better fresh. See Notes below for usage instructions.
Notes
To Use
You can use a small brush that fits in your palm but I like to use a long handled dish brush for scrubbing the shower, it makes it easier to reach the higher areas and I don’t have to bend over quite so far, putting pressure on my back.
Dip brush in mixture to coat well, scrub anywhere there is build up, mildew or spots.