Slow Cooker Ground Beef Stew

1 pound lean ground beef

1 small onion, chopped

2 cloves garlic, minced

1 (10.5 ounce) can condensed cream of mushroom soup

1 cup vegetable broth

½ cup tomato-vegetable juice cocktail

2 tablespoons sherry wine (Optional)

2 teaspoons Worcestershire sauce

4 potatoes, peeled and diced

1 (8 ounce) can whole kernel corn, drained

1 cup frozen green peas, thawed

1 cup diced carrots

1 (4.5 ounce) can mushroom pieces and stems, drained

1 teaspoon dried celery flakes

1 teaspoon salt

½ teaspoon ground black pepper

½ teaspoon dried marjoram

½ teaspoon dried thyme