So besides the obvious of a frost........when do plants, and trees really stop growing???

[a kennedy]

It’s August 1st already, and I was just wondering when the growing season actually stops???

[Pobeka]

1. Daylength is often the trigger for plants to shut down for the winter too.

I'm not sure if that works the same for biennial and perennial plants, but shrubs and trees often respond to daylength.

[Backseat Driver]

2. I'd surmise plants are just like humans...

They slow and age-out according to their external and internal environment(s), but it ain't over until it's over. Putting the garden to bed prematurely is emotionally painful for me! My routine on the North Forty Inches garden has been Sept 30 and out...hence pot some herbs to bring in (where for sure they'll die, LOL) or cut down/trim short if a perennial, plan to make fried green tomatos and chop up any peppers for the freezer of what's left, as necessary or use up fresh. Pull out the rest by the roots (saddened to see baby cukes). I don't practice cover cropping or winter composting...I know--bad human; adjust/augment soil with fertilizer and organics again in the spring.