What about using soap nuts?
You could also use the soapwort plant or yucca root -- both contain natural detergent properties.
Soapwort (Saponaria officinalis) is a vespertine flower, and a common perennial plant from the carnation family (Caryophyllaceae). Other common names are Bouncing Bet and Sweet William. Saponin is in the roots and the leaves are rich in natural surfactants, which form a natural lather ideal for cleaning the skin. It starts producing lather when in contact with water. In traditional medicine, the roots are used to treat certain skin diseases. Soapwort extracts are also used in cleansers, make-up removers, and shampoos.
Yucca roots have been used by Native American tribes for years to prevent hair loss and dandruff while making hair shiny and beautiful. Yucca root makes a great shampoo and soap because it contains natural saponin, which is an all-natural detergent that softly lathers when agitated with water.