Don't usually use green manure because I try whenever possible to add a crop of something as I harvest another crop....I use a loose crop rotation ie never plant somehing from the same family in the same place.

Would the ideal green manure not be a half-hardy plant that was killed off by the first frost? I don't know, just thinking out loud

I know of one chap who always broadcasts leef beet as he takes out his potatoes, then digs it in after a while