Standard laundry detergents can cause serious environmental problems; some ingredients are toxic to fish, and some, like optical brighteners, may even be toxic to humans. There are good alternative detergents out there, but for those wanting to go even farther, soap nuts are another solution.
Soap nuts have been used in India for centuries for cleaning. The 'nuts' are actually berries from the Chinese Soapberry tree, and contain saponin, a natural cleaner. To wash clothes, you put a couple of soap nuts in a cotton bag, and put that in the washing machine. The soapnuts can be reused a few times, and then composted. Soap nut users swear that they clean just as well as regular detergent, and clothes come out unscented but fresh.
The catch: saponin is best released using hot water, and the best choice for the environment is definitely washing in cold water. Soap nut suppliers like Laundry Tree recommend making a sort of tea or liquid detergent from the soap nuts if you want to use cold water in your laundry machine. (It sounds pretty easy: just soak the soap nuts in hot water overnight, and then use the resulting liquid.)
Have you tried using soap nuts? Let us know!