Put chopped onion, celery and apple in bottom of slowcooker. Mix juice with spicing and garlic. Place the roast in the slow cooker on top of the vegetables. Position carrots around roast. Pour liquid over roast. Cook on low for 6 hours.
Remove the cooked roast to a heated platter, arrange carrots and onions around roast. Tent in foil while preparing sauce.
Drain liquid and apples through a sieve. Push softened apples (they will be like applesauce) through sieve as well. Use a gravy separator to remove fat from liquid. Serve as is, or bring to boil on stove and reduce by half, or thicken as for gravy.