Carrots in a box

I grow them in old cold water tanks and cut down blue barrels which are basically the same thing. I find that 18-24" depth is fine to get carrots up to around 7" long. Sowing seeds in a square grid around 1-2" apart give good results - you can grow far more than you'd think in a given space. Although a bit of an odd shape, this came out of an old galvanised garden incinerator today

Have plenty of deep tubs and grow under environmesh with good results.

Yes, don't forget the environmesh! Also just thought, check out the Home Grown Veg channel on YouTube to see what you can achieve with carrots grown in flower buckets.