At least this is how I use them.
Thanks to Paxye for introducing me to soap nuts however long ago that was. They are affordable, biodegradable and effective (although there is no “whitening” power to washing with them). I buy 1 kg bags that last me more than 6 months (even when I was washing diapers too)! My clothes are clean and not covered in detergent residue and they have no scent unless I add it with essential oils (lavender is my favourite).
You only need a few shells.
Put them in a thin cloth bag or thin sock. If you are washing in cold water you need to “activate” the soap nuts in a bowl of hot water. Out of habit, I do this each time regardless of the temperature of the water.
If you agitate or squeeze them the soap will come out. (I did this for the sake of a picture. You don’t need to do this before washing.)
Simply put the closed bag into the wash after the machine has filled and add a few drops of essential oil if you’d like to give your clothes a faint scent. Take the bag out before it goes into the dryer.
These same soap nuts will wash one or two more loads. Sometimes I’ll add one more shell to the bag before using them again.
I buy my soap nuts from a online store based in Quebec. They have by far the best price I’ve ever seen for soap nuts, even with shipping in mind. A one kilogram bag is usually about $20, although the price is sometimes lower when on sale.