When to cut back Asparagus?

[GBax]

Should i wait until all my Asparagus ferns are brown before cutting them off?
I am in the SE of England and only some are brown many are still green (1frost so far)

Thanks for your help

[Mr Bones]

I expect someone with more knowledge will be along shortly but I wait until they've died right back to brown before cutting them off. They don't, however, want to blow about in the wind causing holes around the stem at soil level.

[Alison]

I usually cut them back when they die naturally but last year they never did do think I cut them down in about January.