This was taken from Ed Rosenthal, who is quite a respected grower, but 2 things I do not agree with: In some parts of the country, such as the gulf coast and parts of southern California, the temperature never dips below 7.2ï‚°C and plants can be grown all year round. In areas that are slightly cooler but never freeze, a cold frame or unheated greenhouse is all that is required to keep the plants growing. Besides temperature, the problem with growing plants outdoors during the winter is that the dark period is more than 12 hours and the plants are triggered to flower. This is a good time to grow a sativa dominant hybrid because these varieties continue to grow even after they have been triggered to flower. Southern California winters can get overnight frost which can kill a marijuana plant. Sometimes, the temps dip down to 25 degrees between the hours of 3-6 am in January. You would need a heated greenhouse. I speak of the LA basin, IDK about San Diego or the desert. Sometimes it snows in the desert. UVB light also affects marijuana potency. The potency of high quality marijuana increases in direct ratio to the amount of UVB light it receives. This is very significant. In California, where the medical dispensaries operate in an unrestricted market; many dispensaries reject fall harvested outdoor material as inferior. They have found it lacks the potency of indoor crops and is a harsh smoke. However, when they were presented with marijuana grown outdoors but forced to ripen August 10, they accepted it as if it were indoor because of its high potency and lack of harshness. I think the harshness results from cool nights. Aint that a buncha bulllshit? But it's true. Some dispensaries have told me I grew swag and want to pay half of what I think its worth. One time, my partner and I paid SC labs an obscene amount of money to have our bud tested. It came out at 20%THC (high grade). And they still told me it was swag. That's when I quit selling to dispesaries and became a caregiver.