Nasturtiums (Tropaeolum majus) have run rampant this year on the allotment. I sowed a couple of dozen under the bean canes last year as a form of companion planting. They self-seeded resulting in a dense mass of foliage extending beyond the bed itself.
 I lifted the carpet of them at one end and they have even shaded out the couch grass. It will make a comeback I'm sure when the Nasturtiums are killed off by the first frosts but T. majus makes a good groundcover when conditions suit. I was under the impression that they have been very leafy but short on flowers. In fact there is a lot of seed on the ground beneath the foliage so the flowering must have been more prolific than I thought.