ambrosia salad recipe

1 cup sour cream - 1 cup whipped topping (such as Cool Whip) - 1 cup mini marshmallows - 1 cup sweetened shredded coconut - 1 cup mandarin oranges, drained - 1 cup pineapple tidbits, drained - 1 cup maraschino cherries, drained and halved - 1/2 cup chopped pecans or walnuts (optional) - 1/4 cup powdered sugar (optional, for extra sweetness)