"By all these lovely tokens
September days are here,
With summer's best of weather
And Autumn's best of cheer."
Helen Hunt Jackson
September = Autumn either on the 1st meteorologicallly, or astronomically at the Autumn Equinox on the 22nd (although this year autumn seemed to arrive around the 25th of August)
The word autumn comes from Latin autumnus and it's use dates back to the C14. In the USA it is known as fall and both autumn and fall were used in this country until the C18.
The Anglo-Saxons called September Gertsmonath, meaning the barley month.
There are generally three consecutive windy days around the middle of the month, millers called these the windy days of barley harvest
Nowadays the grain harvest is usually finished before September.
According to the 2020 almanac day length this month decreases by 1 hour and 57 minutes here in the east of England.
There are a few general weather sayings for the month
September dries up wells or breaks down bridges
September rain is much liked by the farmer
Many haws and many sloes make many cold toes.
Below is a page from "An Illustrated Country Year " by Celia Lewis, showing how the hedgerows will fill with berries during the month.
My list of jobs to do through September includes turning some of my harvests from the garden into preserves for the hamper gifts and for my cupboards.