I was wondering how accurate the last frost date I was using. For my area, the Farmer's Almanac has September 29th. It has no information on how it calculates that date, which piqued my curiosity. I found a site to download historical data for the last ten years (https://climate.colostate.edu/data_access.html) and put the minimum temps for September and October into a spreadsheet, then compared each year. 

As you can see, there's a few outliers early in September. September 29th isn't significant, but October 3rd is when we are likely to start getting temperatures below 32 degrees. I'm going to be using that as my last frost date, but keeping an eye out during September.

Did I mention I'm planting a fall garden? Yes, at a local community garden. I'm going to plant things like radishes and beets, that should be ready to harvest before that frost date. I hope. And I'm going to find some row cover to put on top, just in case.