The late Professor Alan Gemmell (Keel University & BBC Gardeners' Question Time) had a good technique for growing carrots.
1 Thrust a crowbar into the earth, and waggle it around to create a conical hole, about half a metre deep.
2 Fill said hole with John Innes No3 Compost.
3 Plant a couple of seed of a large-growing carrot variety such as St Valery. (Maybe more suitable varieties now available: this was 50 years ago.)
4 Discard the weaker of the pair of seedlings.
5 Win first prize at your local garden produce show.