Slow Cooker Beefy Wild Mushroom and Barley Soup

5 cups sliced assorted fresh wild mushrooms, such as portabella, shiitake, oyster and/or porcini (about 10 oz total)

3 medium carrots, sliced (about 1 1/2 cups)

2 leeks, trimmed, cut in half lengthwise, rinsed and sliced crosswise (about 1 1/2 cups)

2 large cloves garlic, finely chopped

1/2 cup uncooked pearl barley

5 1/4 cups Progresso® beef flavored broth (from two 32-oz cartons)

1/2 cup dry sherry or Progresso® beef flavored broth

1/2 teaspoon dried thyme leaves

1/2 teaspoon salt

1/4 teaspoon pepper