Question:
Must 100% pure honey be certified kosher for Passover? How about the rest of the year? Why?
Answer:
Although 100% pure honey does not require kosher certification during the year, I have seen that the Star-K recommends that only honey that is certified as kosher for Passover be used on Passover. This is because some unscrupulous companies have been found to dilute their honey with corn syrup (which is considered kitniyot and avoided on Passover by Ashkenazi Jews). This has been the case even when the product was labeled "100% pure honey."
I hope this helps. Let me know if you have any further questions.
All the best,
Rabbi Eliezer Zalmanov

a further question. is honey in a jar opened not during pesach okay to use during pesach?
I would say that as long as you are sure that not one crumb of chametz has gotten into it, it is fine. That is why in all the Pesach guides which speak about just such matters, when they speak about the products that are fine to use on Passover, they will always mention 'new jars etc.' - meaning, obviously, not used on a chamtez table.