My neighbours recently had some excavations done, and they disposed of the soil by heaping it on top of the bank in front of our houses. They weren't planning to do anything with the bank after this.  They just left it to grow whatever came along, as it's not really within our gardens.   So, I decided to give the weeds some competition, and bought a cheap bag of Californian poppy seed, and another bag of pink flax (linum grandifolium).    If I'd thought of it earlier in the year I might have gone for native ox-eye daisies and poppies but as the idea only occurred to me in July, I had to grab what I could get. 

I don't know if they will manage to flower again next year or if they will be overrun by brambles, but this year they have provided long-lasting cheery ground cover.