Place the shikakai powder, reetha powder, and flax seeds in medium pot. Add 1.5 cups water and stir to combine.
Bring mixture to a boil, then reduce heat and simmer for 20 minutes.
While the mixture is simmering, line a mason jar or measuring cup with a nut milk bag. If you don’t have one, you can use a mesh strainer and cheesecloth to strain it after infusion.
Remove the mixture from heat and pour it into the nut milk bag, using a spoon transfer any herbs that have settled at the bottom. If you don’t have a nut milk bag, you can pour the mixture into a mason jar.
Allow the mixture to cool for about 20 minutes, then stir in the aloe vera powder and amla powder if using.
Let the mixture infuse for another 10 minutes.
Strain through the nut milk bag. The mixture becomes thicker as it cools, so I recommend straining while it’s warm yet comfortable to touch. If you don’t have a nut milk bag, you can also strain by pouring the mixture over bowl that contains a mesh strainer lined with cheesecloth.
Your shampoo is ready to use.