Something I alway try to do whenever I can, is sprinkle seeds. Flowers always make thousands of them. So at the end of their season in my garden or in anyone else's, I take whatever I can and just go around in my garden or in the woods, in the kind of places I want things to grow, and sprinkle them around. (Fabrice usually helps because the mood's joyful and it's a lovely thing to do.)
The year after, or even the year after that, there are usually some surprises. Like these two lovely plants (in the photograph above) just in front of the step of our tiny caravan. I almost dug them out because they were in the way, but everyone (even the dogs) have managed to step round them, thanks to two well-placed sticks.
The nice thing about spreading seeds around is that once the seeds have grown into established plants they set their own seed you get even more surprises !