I too, make my own laundry detergent, using the same recipe as a previous poster,
[Grate 1 bar of Fels-Naptha
1 cup of Washing Soda (Arm & Hammer) NOT BAKING SODA!
1 cup of Borax]

but I cover the soap in a pan with about 2 or 3 inches of water, and heat on the stove over low heat till the soap dissolves, (about 5 minutes), then stir in the Washing Soda, and the borax, stir till dissolved. You can add some essential oils or soap fragrance oil at this stage if desired, I use lavender, or fresh rain, or a mixture of peppermint and eucalyptus. Then put 4 1/2 gallons of hot water in a 5 gallon bucket, and pour the soap mixture, while stirring, into the water. Cover, let sit overnight, and it will thicken to a gel-like consistency. I scoop out about slightly less than a 1/2 cup for my large capacity whirlpool, and it works great. Low suddsing, good for the HE machines, better for the environment, no plastic jugs, or crazy chemicals. You can purchase the ingredients at most grocery stores, or order on line from soapsgonebuy.com.
It costs around 4 cents per load....