Heat a small amount of oil in a skillet over medium heat. Cook and stir onion and carrots in oil until tender.
In a slow cooker, combine beans, carrots and onion, mushroom broth, bouillon, and bay leaf. Pour in water if necessary to cover ingredients with water. Tie together parsley, rosemary, thyme, and savory, and add to the pot. Cook on Low for 8 hours.
Stir in potato, and continue cooking for 1 hour. Remove herbs before serving.