Soak The Beans In Advance. Sort through beans discarding any shriveled beans. Rinse the beans in a colander, then add to a large bowl. Cover the beans water (the water level should be 2-3 inches above the top of the beans). Refrigerate and soak overnight when possible, or at least 4-6 hours, for best results. When you're ready to make the soup, drain the beans in a colander and rinse before adding to the slow cooker.
Combine. Add soaked beans, carrots, onion, celery, garlic, rosemary, sage, and black pepper to the crock of your slow cooker. Cover with vegetable broth and water and stir to combine. Tuck a bay leaf or two into the soup, then cover with the lid.
Cook on HIGH 4-5 hours for brothy soup and 6-8 hours for thicker, more stew-like soup. (You can also gently mash some of the beans for a thicker soup!)
Finish & Serve. Remove the bay leaves from the soup and discard. Season with salt. Taste and add additional herbs, salt, or pepper, to taste. If desired, stir in lemon juice or vinegar and garnish with fresh herbs before serving.
Store leftover soup in an airtight container in the refrigerator 3-4 days. Or, you can freeze the soup up to 3 months. (Thaw in the fridge before using and keep in mind that the veggies and beans will soften upon thawing.)