Sept 18 with a 10% chance it could happen earlier or later. I am praying for later!

Here is a link that might be useful: USDA frost dates .PDF (Maine starts on pg 79)

AHHHHHHHHHHHH!!!!! I still have perennials to get in that I have been putting off.

Farmer's Almanac says it's Sept. 30. I'm pretty sure they used to say Sept. 15. Global warming?

When we first moved here in 1978 we regularly had frost around Labor Day or shortly thereafter. It does seem to be later for the past few years. Temperatures have come close to freezing a couple of times this month, but no frost yet, so we've already bested the Almanac's prediction :)