The first observance of National Energy Efficiency Day was October 5, 2016. A brief search did not turn up a special page for this day or the origin of the idea. Dozens of groups are involved in promoting it, however.
What Grows On in RI is free for everybody, but well-organized information isn't really free. There are expenses. If you like using the Calendar and find the ProvGardener website useful, I hope you'll make a contribution through my Go Fund Me campaign. And let your friends know about the Calendar!