You can never go wrong with adding onions, carrots and potatoes to Mom's Pot Roast! I usually put the carrots, onions and potatoes in the slow cooker or Dutch oven all at the same time. You can also wait until about an hour before serving to add the carrots to the cooking pot. If you want to add sliced yellow or zucchini squash, add them about an hour before the meat is done because they cook faster than the other vegetables.