Carrots in Ikea bags

I'm toying with the idea of growing carrots in the above as the dreaded root fly got at last year's crop on the allotment. What would be a good soil mix? Ta!

 

Good idea Liz, anything above the ground flummoxes them.

Sandy loam with very little stones in an ideal world. Carrots originally come from mainly dry thin chalk soils or sandy banks, so bear that in mind.