Purists may sniff that spaghetti has no business ever entering a slow cooker, because pasta won't hold its shape as well as when it's cooked the traditional way. In the get-real world, you may not always have the time or energy to cook with, and clean, both the slow cooker and a large stockpot. As long as you avoid throwing absolutely everything in the slow cooker hours before dinner, you can still create a spaghetti dinner.
Put all of your sauce ingredients into the slow cooker. If it's a meat sauce, brown the meat on the stovetop, then drain it of fat, before going into the slow cooker with the other sauce ingredients.
Put the lid on the slow cooker and set the temperature to High or Low. The optimal cooking times, before adding pasta, is 6 to 7 hours on Low, or 3 to 4 hours on High.
Turn the slow cooker to High, if it isn't already at that setting, 30 to 60 minutes before dinner. Break the spaghetti into halves or thirds, and mix the spaghetti, plus 1 cup of water, to the slow cooker.
Check the pasta about 30 minutes after adding it the slow cooker. Depending on the type and amount of the spaghetti you are using, it may be at the al dente stage at this point, or it may need more time.
Ladle the spaghetti and sauce into a large bowl, and serve.
A standard spaghetti sauce recipe includes equal parts browned beef and canned tomato sauce, as well as a few cups of tomato juice, a small can of sliced mushrooms and seasonings such as salt, pepper, dried Italian herbs, onion powder and garlic powder.
Never put raw meat into a slow cooker. Ground or cubed meat for spaghetti sauce needs to be browned in a frying pan first. Otherwise, the meat might not cook all the way through, raising the risk of food poisoning.