Janet wrote:
Annual or perennial is irrelevant as both die back in winter, so cut
them off at ground level and compost the topgrowth.
Pea/bean roots are best left in the ground because they
have fixed small nodules of nitrogen.

I've always wondered about this nitrogen fixing business. (And I hadn't
realised it applied to peas as well as beans)

Does the root /have/ to be left in, or does it work if you take most of it
out and just leave 'bits' in? Does it help the compost if you compost it?
And what's a beneficial recipient of post-bean sowing? (I've always assumed
beans then brassicas, but I rarely get to test my plans out, as things tend
to get planted in the 'whatever spot is available' location)