Well, me personally. I do decorate for Autumn now - as I said, I only started it last year.
Maybe the third week in September, as there are loads of flowers still about right now - including lots of sunflowers. So I will do it around 22-23 September. (There will still be some flowers, but a few less, as some of the sunflowers will have died off by then...)
Then I will add Halloween stuff to the Autumn display around 25-26 October, and take them down 1-2 November. I LOVE Halloween and get loads of sweets in for Trick or Treat...(And I like to dress up too!) The whole village 'does' Halloween, and some people dress up and walk around 'scaring' the children. 
Then I put up a poppy/Rememberance Day display around 7-8 November, and take it down around 15 November, then the Christmas stuff goes up 1 December.
Christmas comes down around 6 January, then I put a mini Valentines display up for a few days in mid Feb, then an Easter display for the 2 weeks of Easter - the week before and the week after. Then for the summer, the flowers start coming in during May, June, and July, and August, (and I have lots of garden ornaments/quite a big garden,) so nothing else is needed really. Then we're back to September again.
Don't judge me, I know I'm a bit bonkers. 😂
Should the seasons be capitalised? Hmmmm, good question. I do capitalise them! 
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