Quote Originally Posted by Purple Daddy
August 21st is about the trigger date for flowering, light decreases about a minute and a half a day after June 21st.
This would depend on strain and location.

On August 21st in Denver there are 13.5 hours of daylight. By September 21st there are 12 hours and 13 minutes of daylight. Denver can get the first killing freeze as early as the first week of September though usually it holds off until the first week of october.

So if you have a 56 days-to-finish strain, relatively short, I think it would often get freeze-killed early if it started flowering as late as the third week of August if my understanding is correct. I'm a little unsure how the steady shortening of the days affects the days-to-finish though and I could be wrong.

I do know I have pure indica strains that trigger at 15 hours of light outside and Denver never gets a day that long all year so they start immediately. I have Sativas that can't ever finish outside this far north.

I think there are now "autoflowering" strains that don't trigger on day length at all-they just go. They are from the Cannabis Ruderallis family found in Russia recently I think.


Duration of Daylight/Darkness Table for One Year: U.S. Cities and Towns — Naval Oceanography Portal will let you program in your location and get a table of daylight length.