Rinse the beans in a colander.
In a large pot, bring 10 cups of water to a simmer over moderate heat.
Add the rinsed beans, onions, garlic, carrots, oregano, cilantro and ½ teaspoon of salt.
Reduce the heat to low and simmer partially covered, stirring occasionally, until the beans are tender, about 2 hours.
Discard the onion halves, carrots, and herb stems.
Season the beans with salt and pepper, and serve with tortillas, sour cream, and lime wedges.
