The Creek Line House: Magical, Natural, Weed Killing Potion - gallon of plain white vinegar (I've heard of using apple cider vinegar as well, but I don't think it's necessary) cup of salt 2 tablespoons of dishwashing liquid
Heavily newspaper your garden beds before you put down mulch. Weeds cannot grow through the newspaper, and the decomposing paper feeds your soil. Best gardening tip I ever got! Especially if you then put landscape fabric on top of the newspaper.