I remember watching a gardening programme once, ages ago of course but it stuck in my memory. Geoff Hamilton was talking to an old gardener, forget who it was, and he asked him when to transplant plants. The answer was any time, as long as they are free. I have always acted on this and very often pinch a bit of someone else's plants to grow in my garden. My daughter says if everyone did this there wouldn't be any of the particular plant left. My answer to that is they shouldn't grow them where I can reach them then. Such as grown so that some of the plant is outside of their property. Fair game, I reckon.