How hot does it have to get, before...

[Jura]

You'd not catch me in sandals of any sort, and I always wear hose or knee-highs with heels, so it's closed pumps, Oxfords, or boots all year round for me 

[Thighbootguy]

I went to on out doors jam session with the temperature in the upper 80sF (32C) with the humidity in the 80% range (the jam session was ended when it started raining).  I wore shorts and had dug out an old pair of crocks and really felt embarrassed wearing them.  As we were leaving one of my buddies looked at my feet and said, "Where's your boots?".  It seems I have a reputation to uphold.

[mtnsofheels]

Coming from a cooler place in western Canada, it can be boot weather a lot of the time. However, I do notice that I am adjusted to cooler temps generally so when the mercury rises into the 22C/ 70F it gets to be too warm for me in boots. At the other end of the scale, like this past winter it was -20c/ below 0F many days and then it is just too cold to wear any nice knee high boots. In fact, anything below -5C for any period of time is nasty for the toes. April through most of June and then from end of August to mid-Nov.  As several have said which I absolutely agree with is, when I want to wear boots temps do not apply!

[robbiehhw]

Even at the hottest parts of the year in Oregon's central valley when the temp get's close to 100, the evenings rapidly cool off, usually into the 60s if not the 50s Fahrenheit. So theoretically wearing boots works fashion wise for any evening.

Personally once the daytime highs reach the 75-80 mark, i ditch the boots most of the time. My summer wear is mainly sandals, wedge sandals, block heel shoes, flats or converses. (with actual athletic shoes reserved for athletics)