GDD

I'm new to the forums and growing weed in general, as this is upcoming season will be my first year growing. I am just wondering why growers don't use growing degree days when talking about harvesting?i'm a farmer, and where i live there is up to a 200gdd difference this season within the region (within 20km radius of my place). thats 200 hrs of daylight that plant can use. does accumulated heat units in the fall play a factor in finishing? or is it mainly daylight hours .. vancouver had ave 1275gdd, and southern ontario had upwards of 1500-1600. yet all seedbanks i speak with keep pushing auoflowers and 7 week quick flowering strains(which im not really interested in).. yet in bc they grow 8 week strains.. i should easily be able to finish a 8-10 week strain here based solely on gdd..assuming all things being equal in regards to mould and mildew, soil etc... am i missing something? im just assuming that if my gdd are the same as another area growing strain x or y, i should be able to grow it as well, again assuming all things being equal again, as i can amend the soil and control botrytis and mildew etc.. only weather and gdd are beyond my control..
thanks

Growing inside changes sooo much, no bird shit, no acid rain ,animals.As far as feminizing.I always see subtle weird shit with them..the only way to achieve a perfect strain is to do the work.Crack Seeds find true females.Clone these.Im not dissing Feminizing I just don't want any Bruce Jenners in My Spaces...

Auto's don't grow/flower according to season or hours of sunlight, they flower by age only. As far as flowering times, wheather its advertised as a 7 or 10 week flowering time is an estimate from the breeders that really doesn't mean much. I've never heard of gdd thing, but I would guess people don't use it because the mj plants aren't native to the area and can have big differances in growth rate and flowering times. I don't if that answers your question but its my best guess.

You should see buds outdoors by Aug 20. (<14 hours) First freeze maybe around Oct 20...
About 9 weeks....
My experience just south of the 48th parallel.

its a shame no one uses gdd for cannabis. i might start logging gdd vs flowering dates for 43n parralel for my grow. when the plant starts to flower, i will record the gdd. that way, every year i know that if that strain flowered at 1000gdd or whatever it is, it will flower again at 1000gdd the next year. for arguements sake if in 2016 its hot and dry and i reach 1000gdd august 12th, and in 2017 its cool and wet, and i'm only at 750gdd by august first, i know i won't get flowering unitl prob 3rd-4th week of august if i cross reference when i hit 750gdd the year before.i should be able to predict flowering within +-24hrs, weeks in advance.. then i can adjust my grow accordingly.. gdd dictates a huge part varieties of what grape varieties we grow in niagara. i can post my recorded info on here if people are interested in incorporating gdd into their grow. as for frost, i have wind machines and can check inversion layers during potential frost events and mitagate quite easily.