I've been making my own laundry detergent for seven years now and occasionally get asked about the recipe so I thought I'd share it here.
It's easy to make, effective, and inexpensive (costing around $.14 a load). It's been a while since I paid attention to how long this recipe lasts me, but I'd say 9-12 months. Not too shabby!
You can find all the ingredients stacked together at Wal-Mart in the laundry aisle, or scattered a little at most Targets (it's hit or miss for me). You can also buy them all together on Amazon!
One box of 20 Mule Team Borax 65oz
One box of Arm & Hammer Washing Soda (not baking soda) 55oz
Three bars of soap (not detergent) like Fels-Naptha or Dr. Bronner's
1 tub of Oxi Clean (optional- good on stains, but not "natural")
Roughly chop your bars of soap and put in a food processor until they're crumbled into bits around the size of a pea or smaller.
Combine all ingredients into a 2 gallon canister (something like this) for use. I pour in half the ingredients, mix, pour in the second half, and mix again. It makes a lot!
Use around 1 Tablespoon per load.