Season pork roast all over with salt and black pepper and place in a slow cooker. Spread garlic over pork; add carrots, potatoes, onion, and celery to slow cooker. Pour broth over roast and vegetables.
Cook on High for 2 hours. Baste roast and vegetables with broth cooking liquid; continue cooking on high until tender, 2 hours more. Let rest before slicing, 5 to 10 minutes.
