With carrots, soil prep is the secret to getting a harvest of pretty roots. Carrots need soil that’s free and clear of obstacles—stones, pebbles, sticks—to a depth of at least 6 inches (more is better). Lack of buried obstacles helps ensure straight roots. Otherwise, when a carrot hits a pebble, it shifts and becomes misshapen. The soil should be rich in organic matter so it retains moisture. Clay soils are particularly difficult to grow carrots and definitely benefit from heaps of organic matter.