Before you all throw away or compost your broad bean haulms I have a tip from an old gardener for you.
When you prepare your onion patch lay the haulms at the bottom of the trench with a good handful of bonemeal. Then in the top layer of soil mix in some manure and some more bonemeal.
We do this when the first lot of beans for the autumn sown and then use the later beans for the maincrop.
We all have our own ways of preparing our onion beds but this info may help someone