Beginner Gardening: Carrots: what did I do wrong?, 1 by Gymgirl

Gymgirl wrote:
Allieninja,
You might try again using 18-gallon Rubbermaid tubs with drainage holes drilled in the bottoms and sides near the bottoms. You'll have more than enough depth. Use a loose growing medium, like the recommendations above, and keep moderately moist, but not wet. Also, make sure to THIN your seedlings, as overcrowding can stunt your growth in a different way.

I'd say you're soil was too hard for the carrots to push through easily...