Garlic advice

I have some self seeded/grown garlic which is healthy and green. Because I thought this merely a supermarket cast off that has taken to the garden and decided to stay, and has very small cloves, I decided to buy some Casablanca cloves and try to grow garlic properly.   The Casablanca were started off in pots in early March then transplanted to their growing place in late March.  Now they are going brown and withering.  What do you think I've done wrong.  The onions and shallots in the same area are fine.  If you would like pics, can do.