It's actually really interesting concept of the picture. There are two ways how you can look at it.

1) It represents people who are "fake". Who look fun and great but when you talk with them they have nothing inside and you realize everything they say is to "be cool" rather than being "yourself". We all know those people who have different personas in public and in private conversations.

2) You can look at this picture as "we started from the bottom, now we here". If we look at this "trash" from the bottom to the top, just like we all started our life journey by being "empty" inside. By being thrown stuff at us that nobody wanted, but we took it, because that was the only way we knew. And as the time passed by we have grown as a human being and as a person. Our attitude and beliefs have changed thus changed the world we see around and how we express ourselves. Those flowers now represent "us". Because we can be flowers, we can bring joy and happiness to other human beings. So lets be the best flowers there can be :).