Put the peas, onion, carrot, celery, garlic, and stock in a 3-quart pot and bring to a boil.
Lower the heat and simmer, uncovered, for 1 hour.
Puree the soup in batches in a food processor or blender and return to the pot.
Add the barley, bring to a boil, lower the heat, and simmer for 30 to 40 minutes, or until the barley 1 tender.
Add the seasonings, ladle 1 cup servings into 4 heated soup bowls, and serve.
Let the remaining soup cool and freeze for 1 to 2 months.