S.G.
If I ask a question, I send those who answer a flower - for taking the time.
If someone else asks a question, I send a flower to anyone with a really good answer, esp if it is similar to what i would say.
If I answer a question, I like to get flowers - it affirms that people liked what I had to say. Makes me feel better about my response.
But, I don't think you HAVE to. If you haven't paid much attention to the flowers before, then don't worry about it. There are no "flower" police! hahah :)