Pour 1 gallon apple cider or unfiltered juice into a 5-quart or larger slow cooker.
Cut 1 medium orange into ¼-inch-thick rounds. Cut 1 ½ inches ginger crosswise into ¼-inch-thick slices. Add both to the slow cooker.
Add 5 (3-inch) cinnamon sticks, 1 tablespoon whole cloves, and optional spices. To make it easier to serve, place the cloves and spices in a tea ball first, or place in a double layer of cheesecloth or paper coffee filter, gather it up into a sachet, and tie closed with kitchen twine.
Cover the slow cooker and cook until the flavors meld, 4 hours on LOW. (If there are clumps of spices floating at the top that you wish to remove, strain the cider through a fine-mesh strainer or cheesecloth into a large pot.) Keep warm and serve in mugs garnished with more orange slices if desired.
