What to do with Lulav & Etrog after Sukkot?

Researching this and if anyone has an answer about this and the why and history... please let me know.

One answer from Eliezer Cohen at Jewish Magazine:

Since the lulav and estrog were used for a mitzvah,
it is not becoming to
throw them in the garbage as if they were trash.
Instead we put them aside until Passover. On erev
Passover we take them out and use them to make the
fire to burn our Chametz. Thereby using them to assist
in another mitzvah.

Really want more about this....