There was a good discussion of both “indian summer” and “indian giver” in this thread from last year: Which side is the term "Indian Giver" perjorative towards? - #36 by Son_of_a_Rich
But it doesn’t look like a consensus was reached on whether “indian summer” is indeed pejorative. I guess best avoided if in doubt. “Little summer” seems like a reasonable alternative.
Whatever you call it, it was responsible for my grass needing another mowing.
Wikipedia says:
The phrase may be more acceptable because this warm spell is almost always welcome. Certainly, as a kid, I associated “indian summer” with good things. And hey, maybe the origin is “this extra bit of summer we get here in India”, which wouldn’t be offensive at all.
As a SoCal native, I’ve never used the term.
Do you even get frosts in SoCal?
Isn’t “the extra bit of summer you get in India”, well, the entire year?
We did, especially in the desert. But the phrase was not one I grew up hearing. I don’t think I’ve heard it here in Washington, either.
Unfortunately, I can’t find a direct cite (I find various people Take Our Word For It Archives H-J referring to “The Dictionary of Word and Phrase Origins” by William and Mary Morris as their cite for the idea, but a suitable excerpt isn’t available online).
Therefore I have to admit that I could be wrong - though the line between “the local version of” something and “a substandard or bogus version of something” is a thin one, particularly for colonists who assumed the superiority of all their ways.
Feather India, not dot India. 
Interesting thread, I guess I’d always thought it was hangover from the British Raj, but now that I find it’s American in origin, I’d certainly say it’s in inappropriate. I found an old BBC article on the subject which said
Shakespeare … used the expression “All Halloween Summer” in Henry IV part I for a period of warm sunshine as October gives way to November.
Has a certain ring to it.
It really is interesting because I always thought “Indian Summer” had a British origin and “Halloween” an American one.
The fact I don’t find “Indian Summer” offensive does not mean much. I’ve never thought about it, but am going to start using the phrase “Second Summer” in the rare instances I refer to it.
Pippin : We’ve had one, yes. What about second summer ? Merry : I don’t think he knows about second summer , Pip.
As someone who has a bit better documentation about my Cherokee background than Elizabeth Warren (just messing with you Liz!), I don’t find it personally offensive, and find myself still using it on occasion. That said, I know better than to speak for all Native Americans and will definitely start working on removing it from my vocabulary.
We’re enjoying a lovely second summer in Atlanta at the moment!
What about Novemberses? Yuletides? Mid-winter thaws? He knows about them, doesn’t he?
Second Summer sounds like a decent replacement.
We’ve had a beautiful second summer the last several days.
Actually, it’s a period of of unseasonably warm weather that occurs after the vernal equinox and after a hard freeze.
A different one (live Mazzy Star/Opal version, originally done by The Doors).
(Emphasis added.) Nitpicking because I think you meant “autumnal”. (True, “second summer” or “Indian summer” does fall a fortiori after the vernal equinox too, but then so does the entire regular or first summer, so it wouldn’t be particularly useful as an identifying characteristic.)