After finely grating the bar of soap, add it to a bowl along with the borax,washing soda, and baking soda.
Whisk together very well to make sure it is all evenly distributed.
Put in an air-tight container to prevent clumping.
Use 2-4 tablespoons per load for regular machine, and 1-2 tablespoons for an HE machine.
If washing with cold water, mix detergent with warm/hot water first to help it dissolve and not stick to clothes. I just add the detergent to the washer and run it on hot water until it starts to fill up, and then switch it to cold water and add the clothes.
Recipe by Nature's Nurture | https://naturesnurtureblog.com/powder-laundry-detergent/