The onions you buy in the UK are day length sensitive, so they either need to be planted in March for an late summer harvest or around October, for harvest the next year. I think that is the problem with them. The cabbage won't grow much now and will try to seed in the spring so eat it whenever you like.
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I suspect thats also why my broccoli didnt sprout perhaps - too much manure. But I have been eating the leaves so not a complete waste.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.