Things to Check

Usually, the growing tip of the young carrot hit something or was damaged and couldn't continue straight down. Stones, clods and compacted soil are common causes. Transplanting carrots can also disturb the developing taproot and cause distortion. When thinning carrots, don't waste time trying to transplant the tiny seedlings

How to Fix It

Make sure you have deep, well drained rich soil. 

Add compost to soil mix or some sand if needed. 

Do not add sand to clay soil, as it will form cement. 

Dig in organic matter and turn soil over to a depth of 8 - 10 inches. Rake out rocks. 

Water very deeply and allow mature plants to dry out completely before watering again. 

Do not feed heavy nitrogen at any stage of growth.