The Nasturtiums that carpeted a large patch of the allotment around the bean canes have run their course. They flowered for months and seeded copiously (having grown from self-seeding last year). 

 Nasturtiums are not usually classed as a green manure like Phacelia or Buckwheat but they grow so well on the allotment that they do in effect serve that purpose. The mass of decaying tendrils will add a good amount of humus and nutrition to the soil.

 The humble Nasturtium has edible leaves and flowers, and I gather the seeds can be pickled in brine when still green. It's reckoned to be a good choice for companion planting, attracts bees and makes for a moisture retaining weed suppressing groundcover during the growing season. And a green manure/mulch at the end of the year. Nasturtiums give a lot for very little effort.