Using a slow cooker has many benefits, including the convenience of knowing that dinner is cooking while you are engaged with other tasks. Slow cookers use less electricity and gives off less heat than an oven. The direct heat, steam, lengthy low-temperature cooking and a tightly-closed cooking environment produce a tender, juicy pork roast that shrinks less during cooking. Packaged onion soup, with its premixed seasonings and spices, is another cooking convenience that saves time and effort.
Thaw your pork roast, if needed, which should be large enough to fill the slow cooker at least halfway and not more than two-thirds. You may choose a pork loin, pork shoulder or other large cut of pork.
Set the slow cooker to the medium-high setting. Use a rack in the bottom of the cooker if you want to raise the roast above the drippings.
Place the roast in the slow cooker and add a cup of water. If you intend to cook vegetables -- such as carrots and potatoes -- with the pork roast, add them to the slow cooker first and set the roast on top of the vegetables. Vegetables take longer to cook than meat, according to the USDA.
Sprinkle the onion soup mix over the pork roast and, if you prefer, add a tablespoon of minced garlic and a sprinkle of black pepper. You may also rub the onion soup mix over the surface of the pork roast.
Cook the pork roast for four hours if your roast is 2 pounds or less. Add one hour for each pound over 2 pounds. Keep the lid closed on the slow cooker unless you are stirring the roast or checking to see if it is done. Avoid overcooking by making sure some liquid remains in the slow cooker. You can safely set the cooker to a lower setting for all-day cooking.