One of my favourite "invasive" plants. Trailing Bellflower (Campanula poscharskyana) was introduced to the UK from the mountains of the Caucasus as a rockery plant and quickly decided the brick, stone and concrete of London was just like home.

 It spreads, sprawls and scrambles at the front and back of and back of the house without doing any damage (it has to be said that some invasive species can create problems in that regard). Like many prolific plants it is often treated as a weed but the masses of pale blue flowers in late May/early June are glorious. Ironic that C. poscharskyana is also sold at garden centres- here there's a couple of hundred pounds' worth growing free of charge!

 Both bumblebees and honeybees love Trailing Bellflower and the profusion of flowers is ideal for them, not only at this house but up and down the street and all over town.