They’re not very edible once they get to that stage. The old husbands’ tale is ‘You didn’t dig your soil over properly prior to planting your carrots, and that caused them to fork’. They thought the compaction of the soil and small stones present caused the carrots to deform. What really causes this problem is when you grow carrots in the same spot in your garden every year, you get a fungal disease in your soil, a type of pythium fungus that attacks the growing tip of the base of the carrot. This fungus can also cause sunken black spots along the sides of the carrots. So rotate your crops every year. Ensure that your soil is neutral around a pH of 7 and that it is well drained.