Bingham and Bonneville Counties are Hardiness Zone 5???!!??

[banjomike]

Shades is right.
While Zone 5 plants can thrive here for years with a minimum of cautionary protection, there's always the odd early frost in early September that can kill them.
Even rarer is the odd chinook. We had one back in 2005; all the plants that had just gone dormant, especially roses, woke up and then got frozen solid when the weather suddenly turned very cold again. Folks, including me, lost all their roses and lots of saplings and young trees.

Really a lot depends on the particular location in Idaho Falls. There is more elevation differences inside the city that most folks realize; the entire east side of town is higher than the west, and parts of the east side are much higher. My own home rests in what was once the Crow creek canyon, a creek that still exists, but is now totally piped in by storm sewers, and the canyon was slowly filled by construction rubble and excess topsoil and fill taken out of other subdivisions when I.F. underwent a huge housing boom in the 50s- early 60s.

I used to live down on the other end of my street when I was young. We bought that house when I was 9, and I used to play here with a friend when this end was still wild and undeveloped. Even though this end of the street is much higher than the other end, my house is in a lower spot than all the surrounding houses. I can grow Zone 5 plants my immediate neighbors can't.