Cauliflowers and trays

How deep do cauliflowers send their roots?  I'm using 5" deep wooden trays for salads etc but don't know if my caulis need something deeper ...

And what other crops can people suggest that I can grow in my trays?

All brassicas need a lot more depth and also they need to be trodden in quite firmly, so I would'nt recommend you grow them in trays.

Aah ... thanks for that Agapanthus.  I've not grown brassicas before so had forgotten about the treading in ... though it could make a good piccy  

Am certainly going to grow some herbs in the smaller trays, along the front of my patch (don't have an allotment  :cry: just a patch that I'm creating on my patio)  but I've also got some slightly larger boxes - fancy trying something a bit unusual but not sure what else I could get away with ...  what about swiss chard??