PopSugar and MommyPotamus.com each have recipes for liquid laundry soap. PopSugar's recipe is a slightly diluted form of Dr. Bronner's Castille soap mixed with washing soda, whereas the MommyPotamus.com recipe combines the essence of soap nuts and a mildly acidic component.
To prepare PopSugar's liquid laundry soap, whisk together 1/2 cup Arm & Hammer super washing soda and 1/4 cup Borax in a large bowl. Continue whisking while adding 1 cup of boiling water. Stir to dissolve the dry ingredients.
Add 1 tablespoon liquid castile soap, 1/4 cup distilled white vinegar and enough hot water to fill a gallon jug. Transfer the liquid soap to a gallon jug via a funnel. Though essential oil is optional, add 10 to 20 drops to personalize the detergent.
The MommyPotamus.com recipe for liquid laundry detergent contains 24 to 30 soap nuts, 12 cups water, 1 teaspoon citric acid or 2 teaspoons salt, and 16 to 20 drops of essential oil, such as lemon or tea tree. Add the water and the soap nuts to a large pot set over medium heat. Bring the uncovered pot of water to a boil, reduce the heat, cover, and simmer for approximately 60 minutes.
Remove the pot from the heat, let the water cool and strain out the soap nuts. Dissolve the citric acid or the salt in hot water, and then add it and the essential oil. This recipe yields roughly 24 ounces or enough for about 12 to 14 loads.