Some are very close to constant. Roses, for example, are pretty much always the same.

[She started to get the trough ready for Nagi to put the plant down before stepping back and nodding to it. She gave a wistful sigh before starting on the next one right afterwards.]

The colors and meanings of roses haven't changed any time I can recall. It's some of the others that seem to shift. I think part is because now everyone has access to new flowers? Though, it's fairly static in japan. They never change there, except to add new flowers.