If your split peas are still crunchy, they need to cook longer. Check them periodically and add additional broth, if needed, so they remain covered in liquid through the cooking process. Just like dried beans, split peas require a slow, long cooking time in order to become tender. When cooked in a slow cooker, the dried peas will break down and transform in front of your eyes into a beautiful, thick and creamy soup over the course of 8 to 10 hours. The longer you let them go, the creamier your soup will be. And, this my friends, is a good thing!