You can give away your flowers and trees.

Better not. First, some people believe in Feng Shui theory, and the flowers and trees they raise may be related to their own fortune. If you don't believe it, and neither do the people who give it to plants, then there is no such thing. Secondly, I won't give away my own plant unless I know this person well enough to be sure that he likes this plant and can take good care of it. So you can send it, but you can't "casually".